Chm 222 - Smith Collegerlinck/Chm222/sec/pset2.pdfChm 222 Spring 2016, Exercise Set 2 Mass...

Chm 222Spring 2016, Exercise Set 2

Mass SpectroscopyInfra Red and

1H and 13C NMR

Mr. Linck

c©Boniface Beebe ProductionsJanuary 4, 2016

Version 4.1.

NOTE: An asterisk in the problem title indicates that it is a continuing problem from theprevious one. Two asterisk tells you the problem depends on the last two, etc.

2.1. Learning Organic Chemistry

Review your notes for the course to this point. Organize into major topics and sub-topics.Your organization may not be chronological; in fact, it would probably be better if it wasnot.

2.2. Review of Reaction Type

Identify the type of reaction (“addition”, “substitution”, or “elimination”) for the following:

(CH3)2CHCBr(CH3)2 + (CH3)3CO− = (CH3)2CC(CH3)2 + (CH3)3COH + Br−

What kind of compound is formed in this process? HINT: In an organic chemistry coursewe focus on the “organic” molecule. In this case, that is the first one mentioned, not thesecond, which merely serves as a base.

2.3. Mass Spectroscopy

We use mass spectroscopy only slightly in this course. The key to our usage involves themolecular radical ion which is the molecule with one electron knocked out. It is an ion,a cation to be precise, because of the loss of that electron. It is a radical because it hasan odd number of electrons. Since the mass of the electron is small compared to that ofnuclei, the mass of the molecular radical ion is essentially the same as that of the unionizedmaterial from which it arose. Although modern spectrometers are capable of distinguishingmore finely, we shall stick with “integer” mass units: CH4 would have a peak at 16 massunits. With that information, you should be able to handle problems such as this and thefollowing ones labeled “Mass Spectroscopy”: Octane would have a molecular ion peak atwhat mass number?

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At what mass numbers would the M+. peaks be for the following compounds: C5H10O,C5H8F2, C3H6?


After the electron is removed, the molecular radical ion can also break into smaller frag-ments. The ions of these fragments are also detected in the mass spectrum. Hence we havea number of peaks of mass of the molecular radical ion and peaks of smaller mass. In themass spectrum of a compound there are major peaks at 27, 39, 41, 55, 56, 69, and 84. Ifthe compound contains only C and H, what is the formula? HINT: Find the M+. peak anduse ihd.

2.6. Mass Spectroscopy and the Isoelectronic Relationship

Why do compounds with an odd number of nitrogen atoms have an odd mass number forthe molecular ion when the mass of N is 14. HINT: Think about typical groups that areisovalent with the NH2 group.


For Br, there are two common isotopes, 79Br and 81Br. These occur in nearly equal quanti-ties in nature. These peaks are usually called the M+ and M+2 peaks, which is a nomencla-ture of convenience and does not mean that the second peak is dipositive. Work your waythrough what the meaning is. What would the masses of the molecular ions be for ethylbromide and what are their relative intensities? HINT: Look carefully at the grammar ofthe question, especially the (correct) use of plurality.

2.8. Mass Spectroscopy*

A compound has molecular ion peaks (judged to be so because there is nothing at a highermass number) of 136 and 138 of about equal intensity. Make an intelligent guess as to theidentity of the compound.


A compound has “molecular” peaks in the mass spectrum at 135 and 137 of about equal in-tensity. What can you say about this compound? HINT: Think. There is more informationhere than what first meets the eye; try to find it all.


The common isotopes of Cl are 35Cl and 37Cl; the former is three times as abundant as thelatter. What would the masses of the “molecular ions” be for 3-chlorohexane and what aretheir relative intensities? HINT: Again, the use of a plural.

2.11. Mass Spectroscopy and the M+1 Carbon Peak

There is an isotope of carbon, 13C, which has an abundance of 1.1%. This means that forevery 1000 carbon atoms, you will find 11 atoms with the heavier isotope. If you had a10000 molecules of CO2, what is the chance that you would find one with a weight of 45?


If you had 100 molecules of C2O4H2, what is the probability that you would find a moleculeof this substance with a mass of 91? HINT: A little trickier: 100 molecules contains 200atoms of carbon.

Chm 222 Exercise Set 2

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Compounds of carbon with lots of carbon atoms often show a small peak one unit in masshigher than the molecular ion peak due to the 1.1% of carbon that is 13C. If you have acompound containing five carbons (each of which has a 1.1% chance of being a 13C, whatwill be the relative height of the M+1 peak relative to the M peak. HINT: Extrapolatefrom the last two problems.


From the last several problems you should be able to deduce that the following formulagives the number of carbon atoms in a compound, nC .

nC =

IM+1

IM

0.011

where IM and IM+1 are the intensities of the M and M+1 peaks, respectively. Do so.


A compound has “molecular” peaks in the mass spectrum at (mass, (intensity)) 76 (25.3);77 (0.9); 78 (8.0); and 79 (0.3). What can you say about this compound? HINT: Thiscourse is trying to get you to put arguments together to arrive at a logical conclusion.


If you didn’t already obtain two facts about the compound in the last problem, do so now.Use the M and M+1 peaks to estimate the number of carbon atoms or use the fact thatthere is a M and an M+2 peak.

2.17. Scientific Consistency**

As a good scientist you should always make sure your data is consistent. In the last twoproblems, you have established two things about the molecule. Are those things consistentwith the observed molecular mass?

2.18. M+1 Peak in Mass Spectroscopy

A substance of formula C8H16O has a molecular ion peak in the mass spectrum with inten-sity of 24.3. What would you expect for the intensity of the peak at M of 129?


A compound has a mass spectrum with peaks at 186 and 188 of equal intensity, say 100,and a peak at 189 of 7.8. What can you say about the compound?


The compound in the last problem has additional peaks in the mass spectrum: at 171 (51units), 173 (52 units), and 174 (3.4 units). Can you say anything about what fragment waslost from the original molecular ion?


Here are some “fudged” data, manipulated to make your analysis easier. A compound hasmass spectrum peaks at 92 (intensity = 70.0) and 93 (5.5). How many carbons are in thematerial?


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2.22. More Complicated Mass Spectroscopy*

Here is the real data for the compound in the last problem. The peaks and intensities nearthe molecular ion peak are: 91 (100), 92 (77.7), and 93 (5.5). Figure out why and how I“fudged” the data. Be sure you see that because I “fudged” the data in the last problem,that problem was much easier than it might have been. HINT: Think about the number ofcarbons likely in that peak at 91 and the consequences for the peak at 92.

2.23. Mass and IR Frequency

The frequency at which a peak occurs in the IR spectrum caused by a bond stretch isgoverned by the equation:

ν =1

2π

√k

µ

where k is the force constant, a measure of the bond strength, and µ is the reduced mass,

equal to(

m1m2(m1+m2)

). Why do C-H, O-H, and N-H bond stretches occur at higher ν than

C-C, O-C, or N-C stretches?

2.24. Bond Strength and IR Frequency

Generally the C-H bond of an alkyne is stronger than that of an alkene, which is strongerthan that of a alkane. If the first of these absorbs near 3300 cm−1, where would you expectthe others to absorb?

2.25. Bond Strength and IR Frequency

Why does a carbon-carbon double bonds stretch occur at higher ν than a carbon-carbonsingle bond stretch?

2.26. Double versus Single Bonds in IR

Where would you expect double bonded carbon-oxygen (C=O) stretches to occur relativeto single bonded C-O stretches?

2.27. Triple versus Double Bonds in IR

Where would you expect the stretches of triple bonded carbon-carbon species to occurrelative to double bonded carbon-carbon molecules?

2.28. IR Frequencies

Where would you expect double bonded carbon-sulfur stretches to occur relative to doublebonded carbon-oxygen stretches? HINT: If there are multiple factors, and there are in thisquestion, then you should examine all of them.

2.29. Estimating IR Frequencies

The carbon-carbon stretch in alkynes typically occurs between 2100 and 2300 cm−1. Ap-proximately where would you expect nitriles, such as CH3CH2CH2CN, butanenitrile, toabsorb?

2.30. Using IR to Identify Functional Groups

You have two compounds of formula C6H12. Compound A has peaks in the IR at 3016,2861-2961, 1658 cm−1 and a bunch of stuff in the region below 1500 cm−1. Compound Bhas peaks at 2853-2928 cm−1 and a bunch of stuff below 1500 cm−1). Which is cyclohexane?Why do you reach this conclusion?


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2.31. IR and the Scientific Method

You are analyzing an IR and find a rather weak and narrow peak near 1675 cm−1. Giventhe weakness, should you ignore it or instantly check elsewhere in the spectrum? HINTS:(1) Why would I ask if the answer wasn’t obvious? (2) Learn to “pursue” your analysis toconclusions that are certain (First of many times this will be said.).

2.32. Coupling in IR

If the value of ν for a E-X stretch is close (in energy) to that for a E-Y stretch (where Eis some element and X and Y can be the same element), they often “couple” to give, forinstance, a symmetrical stretch (X and Y both moving away from the E at the same time)and an asymmetrical stretch (X moving toward the E as Y moves away, and the reverse),each with a slightly different ν. Compounds containing an -NH2 group have two peaks near3300-3400 cm−1. Why?

2.33. IR Interpretation*

The IR spectrum of dimethylmalonate, CH3OC(O)CH2C(O)OCH3, has, not surprisingly,a peak in the 1740 cm−1 region. Why? This peak is, however, considerably broader thannormal carbonyl peaks. Why is this so? Make an intelligent guess.

2.34. Learning the IR Positions

How many peak positions in the IR, between two elements, neither of which is a hydrogenatom, are there? At what wave number is each? Is one slightly broader than the others?Is one generally stronger than the others? Is one usually quite weak? HINT: I mean, ofcourse, peaks you should know about, those greater than 1500 cm−1.


How many peak postions in the IR, between X-H, are there? Which are narrow and whichare broad? At what wave number is each? HINT: I mean, of course, peaks you should knowabout.


How many peak postions in the IR should you know? At what wave number is each?

2.37. IR

What can you say about the following compounds given their IR spectra in the functionalgroup region (all reported in units of cm−1). A 3410 sharp, 2900-3000, 2150 sharp, butweak; B 3400 broad, 2900-3020; C 2850-3000, 2710, 1725.

2.38. IR Peak Detail

Generally speaking, the broad O-H stretch in alcohols occurs near 3300 cm−1 and does notinterfere with the peaks due to C-H stretches, whereas the broad O-H stretch in carboxylicacids usually occur at a lower wave number, nearer 3000 cm−1 and hence does overlap withC-H stretches. This can be used to determine which of the two kinds of O-H group ispresent. A compound of the formula C9H18O2 absorbs with a broad peak near 3020 cm−1.What might the compound be?

2.39. Review of Carbon Level

What carbon level is the carbon atom in CH2O? What carbon level is the carbon atom inCH3OH?


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2.40. Review of a Reaction

What is the product when CH2O is treated with 1) BH–4 followed by 2) H+?

2.41. Changing Carbon Level*

In the last problem the carbon level changed from 2 to 1 upon treatment with an H–

equivalent followed by H+. We could say that the carbon level was reduced by H– and H+,which is electronically equivalent to H2. What reagent lowers the carbon level? HINT:There is a specific answer, rather obvious, and a generic one, involving oxidation states,only slightly less obvious.

2.42. Changing Carbon Level

Write a balanced reaction for the lowering of the carbon level of CH2O by one unit withH2.


Write a balanced reaction for the raising of the carbon level of CH3OH by one unit withO2 (half a mole).

2.44. Raising Carbon Level and Electron Acceptors

Oxygen molecules are good electron acceptors. Why?

2.45. Raising Carbon Level and Electron Acceptors

Generally speaking, species that want to gain electrons are likely to be able to raise thecarbon level of an organic molecule. Which of the following would you expect to be a goodelectron acceptor (or speaking professionally, a good oxidant): F–, F2, H2O, O3, Cr2+,CrO2–

4 (a Cr(VI) compound), MnO–4 (a Mn(VII) compound)?

2.46. Carbon Levels

What is the carbon level of the interesting carbon in 3-hexanol, C6H14O? of 3-hexanone,C6H12O?

2.47. Reaction and IR

A student treats 3-hexanol with PCC (a Cr(VI) compound officially called pyridiniumchlorochromate, C5H5NH+CrClO–

3, which we will use extensively later in the semester; itis a good oxidizing agent) to try to form 3-hexanone. What should she look for in the IRto verify that reaction occurred? HINT: Remember a good scientist looks for confirmationof observations.

2.48. Reaction

What is happening in the following reaction? HINTS: (1) An answer in several differentmanners would be nice: carbon level; oxidation/reduction; kinds of compounds destroyed,formed. (2) Unless you are sure what you are seeing, write out the reaction in our normalline (zig-zag) form.

CH3CH(OH)CH2CH2CH3PCC−−−→ CH3C(O)CH2CH2CH3


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2.49. Synthesis

How would you prepare propanone, CH3C(O)CH3, from 2-propanol, CH3CH(OH)CH3?HINTS: (1) The procedure is to ask 1. “What kind of compound is the one that I desire tomake?”, and then 2. “What ways do I know to make that kind of compound?” (2) Then, ifyou haven’t figured out the answer, you might ask, “Is there any method that I just learnedthat maybe this question is reviewing?”


What is happening in this reaction? HINTS: (1) An answer in several different mannerswould be nice: carbon level; oxidation/reduction; kinds of compounds destroyed, formed.(2) Unless you are sure what you are seeing, write out the reaction in our normal line(zig-zag) form.

CH3C(O)CH3

1.BH−4−−−−→

2.H+CH3CH(OH)CH3

HINT: The notation 1. blah blah, 2. yap yap means add the first reagent, wait for reaction,then add the second.


What is happening in this reaction? HINTS: (1) An answer in several different mannerswould be nice: carbon level; oxidation/reduction; kinds of compounds destroyed, formed.(2) Unless you are sure what you are seeing, write out the reaction in our normal line(zig-zag) form.

CH3C(O)CH3

1.CH3MgI−−−−−−→

2.H+(CH3)3COH

2.52. Review of Synthetic Reactions

How do you oxidize a carbon level 1 compound to carbon level 2 compound? How do youreduce a carbon level 2 compound to a carbon level 1 compound?

2.53. Review of Synthetic Reactions*

There are two kinds of answers to the second question in the last problem. How do theydiffer?

2.54. Synthetic Reactions

Let’s go up a notch. At this point in the course, speaking in general terms, how would youprepare a ketone (what carbon level?) from an alcohol (what carbon level?) with fewercarbon atoms? HINTS: (1) Learn to think your way through problems of this sort if youwant to be successful in organic chemistry. The only way we know to make C-C bonds(at the moment) is to react a ketone or aldehyde with a “C−” reagent, so that must bethere somewhere. (2) Use problem 47 and, when you finish, congratulate yourself for thissynthesis containing multiple steps.

2.55. Synthetic Reactions

How would you prepare 2-butanol from ethanal and ethyl bromide? HINT: Go backwards(officially called retrosynthetic analysis): “How do I make an alcohol?”


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2.56. Reactions

How would you prepare 2-butanone from ethanal and ethyl bromide? HINTS: (1) Gobackwards. (2) Think about the last problem and remember something from problem 47.

2.57. Reactivity and IR

A sample of propanone is treated with CH3MgCl and then H+ in water. What would bethe product of the reaction? How would you detect that reaction occurred using IR?

2.58. Functional Groups from IR

What can you say about the compound whose IR is given in Figure 1?

2.59. An Oxidizing Agent

Ozone, O3, is a powerful oxidizing agent. Draw a Lewis structure of ozone and determinewhy it wants electrons so badly.

2.60. Oxidizing Agents and Carbon Level

Given that ozone, O3, is a powerful oxidizing agent (see the last problem), should it becapable of taking a carbon level 1 compound to carbon level 2?

2.61. Carbon Level

An alkene reacts with H2 to produce an alkane,

CH3CHCH2 + H2catalyst−−−−−→ CH3CH2CH3

Let’s apply some logic. (1) What is the carbon level of the carbon atoms in the product?(2) Given that problem 41 shows that H2 is a reductant that lowers carbon levels by oneunit, what must be the carbon level of one of the carbons in the reactants? (3) The affectedcarbons in CH3CHCH2 must be the last two, as the first is certainly not attached to anythingfunny. Conclusion: Could we say that an alkene is a delocalized carbon level 1 (or, if youlike, each carbon with a double bond to another carbon is carbon level 1/2)? What wouldbe the carbon levels in CH3CH3CHCHCH3? or you might just answer the question for theinteresting carbon atoms.

2.62. Oxidizing Agents and Carbon Level*

Continuing with the logic of the last problem: If an alkene is a delocalized carbon level1 compound, and ozone is an oxidizing agent, what carbon level might the products of areaction between an alkene and ozone have? HINT: There are multiple answers to thisproblem. Take the smallest change.

2.63. Ozonolysis of an Alkene**

A molecule of 2-pentene reacts with O3 followed by treatment with Zn to form a mole ofethanal and a mole of propanal (as we will examine more carefully later). This may be theonly reaction we will learn this semester that cleaves a carbon-carbon bond, and a doublebond at that! Write out a summary of this reaction (from the point of view of the carbonskeletons–the stoichiometry of the process is not simple) and see if you can figure out howto predict what happens when ozone reacts with an alkene and the product is then treatedwith Zn. HINT: Look hard at what you did to solve this problem. I am giving it here inthe hope that it will ease your life later on, but that hope depends on your diligence.


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Figure 1: IR for Problem 58


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2.64. Reactivity and IR***

What would you look for in the IR to determine if the reaction in the last problem occurred?

2.65. Ozonolysis and IR

Predict the product of the reaction of ozone, O3, with 2-hexene followed by treatment withZn. What would you look for in the IR to identify the nature of the products?

2.66. Prediction of Ozonolysis Products

Extrapolate your knowledge by predicting the product of the reaction of ozone, O3, with2-methyl-2-butene, followed by Zn. HINT: An H and a CH3 group are isovalent.

2.67. Reactivity and Hydrogenation

As we saw above, H2 reduces carbon level. The compound 2-butene reacts with H2 inthe presence of Pd metal coated with charcoal (written Pd(C)) to yield butane (as we willexamine more carefully later). This is one of the few ways we will learn this semester thatremoves a functional group from a molecule. Write out the stoichiometry of this process.How would you classify the reaction, “addition, elimination, or substitution”? HINT: Hereagain we have a future reaction that you might try to get used to using.


For the reaction in the last problem, what would you look for in the IR to detect theoccurrence of the reaction?

2.69. Reactivity

What product would you predict if you reacted H2 and Pd(C) with 2-methyl-2-butene?


What product would you predict if you reacted H2 and Pd(C) with 1,3-pentadiene? WhatIR signal could you follow to determine the extent of this reaction?

2.71. Review of Three Reactions

In the past tens of problems we have looked at three reactions. What are they?


What reaction would you use to convert an alcohol into a ketone or aldehyde?


What reaction would you use to convert an alkene into an alkane?


What reaction would you use to convert an alkene into two carbonyl compounds?

2.75. IR Identification of Functional Groups

What can you say about the compound whose IR has, in addition to the normal peaks, abroad peak at 3100 cm−1 and a intense, slightly broadened, peak near 1720 cm−1.


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2.76. IR

What can you say about the following compounds given their IR spectra in the functionalgroup region (all reported in units of cm−1). A 3450-3600, broad with some sharp peaks ontop of it in the 2950-3000 region, 1723 intense; B 3450-3600, broad with some sharp peakson top of it in the 2950-3000 region, 1700 intense, 1650 sharp; C broad peak centered at3350, 3080 sharp,1650, sharp.

2.77. IR Frequency

If I told you that a carbon-fluorine bond stretch occurred at about 1050 cm−1, what wouldyou predict for the frequency of a carbon-chlorine bond stretch?

2.78. IR Frequency*

If I then told you (in addition to what I said in the last problem) that the bond strengthof the carbon-fluorine bond is about 25 kcal/mole stronger than the corresponding carbon-chlorine bond, how would your answer to the last problem be changed?

2.79. IR

Figures 2 and 3 give two IR spectra, both of compounds of the formula C5H10O. Find astructure that is consistent with each spectrum.

2.80. Review of Epwa and Reactivity

Use epwa to show what happens when BH–4 reacts with 2-pentanone.

2.81. Review of Epwa and Reactivity

Use epwa to show what happens when the product of the last problem reacts with diluteH3O

+, also called H+.

2.82. Epwa and Reactivity

Use epwa to show what happens when OH– reacts with 2-propanone.

2.83. Classification of Reactions

How do you classify the net reaction in problems 80 followed by 81? How do you classifythe reaction in problem 82?

2.84. Stability of Negatively Charged Species

Consider H− and OH–. Which compound would you guess is more tolerant of the negativecharge? HINT: Periodicity.

2.85. Reversibility of Reactions

If I told you that the reaction in problem 80 was irreversible and that in reaction 82 wasreversible, how would you explain it? HINT: Note in both cases the carbon species is thesame; what differs is the “leaving group” in the second case. Getting this concept now willmake the rest of the course much easier.

2.86. IR and Reactivity

Propanal, whose IR spectrum has an interesting peak at 1740 cm−1 reacts with a reagentto produce a compound whose spectrum no longer has the 1740 cm−1 peak, but now has aninteresting peak at 3350 cm−1; this peak is broad and strong. What can you say happenedin the reaction? HINT: By “interesting” I mean within the context of this problem.


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2.87. Another Summary of IR: X-H Stretches

Make a summary of the position, intensity, and broadness of peaks caused by various X-Hstretches in the region between 2700 and 3600 cm−1.

2.88. Another Summary of IR: Double Bond Region

Make a summary of the position, intensity, and broadness of peaks caused by variousstretches in the region between 1500 and 1800 cm−1. HINT: I am looking for only twoentries in your list.

2.89. IR and Frequency

The force constants for the C-H bond and the C-C bond are about the same. Yet the C-Hbond stretch occurs at a much higher wave number than does the C-C stretch, which isburied in the “garbage” below 1500 cm−1. Why?

2.90. ihd Review

What is ihd? What does it tell you?

2.91. IR Identification

Two isomers of C4H6O, A and B, are both symmetric. Isomer A has IR peaks at 3090and 1620 cm−1, whereas isomer B has peaks at <3000 and 1780 cm−1. Neither materialabsorbs in the 3300-3700 cm−1 region. Propose structures for the two isomers.

2.92. Use of IR

You would (if you are wise) never use IR to tell the difference between a compound con-taining a C-Cl bond and one containing a C-Br bond. Why not?

2.93. IR and Frequency

If you were pressed on the issue posed in the last problem, what would you say the differencebetween the two would be?

2.94. IR of Carbonyls

Without looking at any tables or books, at roughly what energy (units of wave number) docarbonyl compounds absorb in the IR?

2.95. IR of Alcohols

Without looking at any tables or books, at roughly what energy (units of wave number) doalcohols compounds absorb in the IR?

2.96. IR of Alkenes and Learning Organic Chemistry

Without looking at any tables or books, at roughly what energy (units of wave number)do alkene compounds absorb in the IR? HINT: If you can’t answer the last three questionsyou are not studying correctly in this course.

2.97. Use of IR

Are 2-butanone and but-2-en-1-ol isomeric? Do they have the same ihd? How could youuse IR to distinguish between 2-butanone and but-2-en-1-ol?

2.98. IR Intensities

Why is the C triple bond C stretch absent in the IR of a symmetrical alkyne?


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Why is the C triple bond C stretch weak in the IR of an asymmetrical alkyne?


Why is the stretch of a double bonded C=O of high intensity whereas that of a normaldouble bonded C=C considerably less intense?

2.101. IR

How would you distinguish between compounds 1 and 2 using IR?

2.102. IR of Unknowns

Here are three IR spectra, A, B, and C. Spectrum A: <3000 including 2700; 1722 cm−1;Spectrum B: Broad peak with two maxima 3200-3400, <3000, broad peak 1620-1680 cm−1;Spectrum C: 3110, <3000, 1645 cm−1. Assign each spectrum to one of the compounds 3-7.

2.103. Review of Reactions

What would be the product of the reaction of 2-hexene with H2 over Pd(C)?

2.104. IR*

How could you use IR to tell when the reaction between 2-hexene and H2/Pd(C) wascomplete?


What would be the product of the reaction of 2-hexene with O3, followed by Zn?

2.106. IR*

How could you use IR to tell when the reaction between 2-hexene and O3, followed by Zn,was complete?


What would be the product of the reaction of 2-hexanone with BH–4, followed by H+?


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Table 1: Chemical Shifts of Methine, Methylene, and Methyl Groups, in δ.

X- X-CH-R2 X-CH2-R X-CH3

RCH2- 1.5 1.2 0.9

F- 4.8 4.45 4.25

Cl- 4.05 3.45 3.05

ClCH2- 1.95 1.80 1.50

HO- 3.95 3.55 3.2

RCC- 2.8 2.2 1.7

C6H5O- 4.5 4.05 3.85

RC(O)- 2.65 2.3 2.1

2.108. IR*

How could you use IR to tell when the reaction between 2-hexanone and BH–4, followed by

H+, was complete?


What would be the product of the reaction of 2-hexanone with CH3MgI, followed by H+?

2.110. IR*

How could you use IR to tell when the reaction between 2-hexanone and CH3MgI, followedby H+, was complete?

2.111. IR and Mass Spectroscopy

A molecule is isolated from a biological sample. It has the following IR: a broad peakbetween 3200 and 3600 cm−1 and two peaks in the region between 1600 and 1700 cm−1.What functional groups are in the molecule? The mass spectrum shows a M+1 peak withrelative intensity of 3.9 and a M peak of intensity 27.2. How many carbons are (likely) inthe molecule?

Here we begin our analysis of NMR structure determination.

2.112. The Basis of NMR Shift

All bare protons in a magnetic field of fixed strength have a transition between the two spinstates (up and down) at the same energy. Why do hydrogen atoms in different environmentsin molecules have signals at different energies?

2.113. NMR-Chemical Shift

Table 1 gives the chemical shift (in units of δ) of compounds with methyl, methylene (-CCH2-), and methine (C2CH-) hydrogen atoms. For instance, the signal due to the methyleneprotons in CH3CH2OH would occur at approximately 3.55 δ. What do you learn about therelative chemical shift of methine versus methylene versus methyl hydrogen atoms when theX group on the carbon is the same?


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Table 2: Chemical Shifts of Various Fragments

Fragment δ Fragment δ

alkene-CH3 1.7 C6H5-H 6.5-8.0

alkene-H 4.5-6.0 C6H5−CH3 2.3

alkynyl-H 2.5 C(−−O)−H 9.0-10.0

R−NH2 1.5-4.0 RC(O)O−H 10-12

RCH2O−H 2-5 C6H5O−H 4-7


What do you learn about the position of a CH3C(O)R signal? HINT: When I see a δ 2.1signal I hear “ding, (pause), ding, (pause) ding” and I burst into song: “It’s three o’clockin the morning, we’ve danced the whole night thru . . . ” written by Theodora Morse (asDorothy Terriss) and Julian Robledo in 1921.


From Table 1, what do you learn about a CH3-C signal compared to a CH3-O signal? HINT:The professional would use words like “down field” or “up field.”


From Table 1, what do you learn about a -CH2R signal compared to a -CH2-Cl signal?HINT: R is some unspecified collection of C and H atoms, which is “innocent.”


From Table 1, what do you learn about the methyl group signal in CH3CH2Cl compared tothe methyl group signal in CH3Cl? What would you predict for the methyl group signal inCH3CH2CH2Cl?


Summarize in a concise manner what you learn from a careful study of Table 1.


Table 2 lists the chemical shift of some hydrogen atoms in compounds that you shouldknow. NOTE: All data are approximate and will vary from molecule to molecule. Similardata is also available on the chemistry department web page under “Resources”. If you hada compound with a signal near 5 δ, what structural feature would you suspect was in yourmolecule?

2.120. Learning How to Verify*

Would there be any information that would aid you in your answer to the last question?What would that information be?


True or false? If I told you that there is a signal in the 1H nmr at 4.0 δ, you would bejustified in saying “This molecule contains an ROH group.” Give your reasoning.


2.128 18

Table 3: Electronegativity and Chemical Shifts

E χ δ

F 4.0 4.3

Cl 3.2 3.0

Br 3.0 2.7

I 2.7 2.2

OH 3.4 3.4

NH2 3.0 2.36

SiH3 1.9 0.04

BeCH3 1.6 -1.0


Which of the following hydrogen nuclei would you expect to have a signal at higher field(near TMS, that is, (CH3)4Si), lower δ, and which at lower field (near CHCl3), higher δ?a. R2BCH3, b. CH2F2, c. CCl3CHClCCl3, d. N(CH3)

+4 . HINTS: (1) “R” is just some

unspecified collection of carbon and hydrogen atoms. (2) Be careful with the last compound;think about what causes chemical shifts.

2.123. The Fickle -OH and Learning Organic Chemistry

Boniface Beebe, the highly admired natural philosopher of Searcy, Arkansas, wrote: “I havean proton with a signal at about δ 4.0. There must be an ‘H of an OH’ in my sample.”What would you say to Bonnie?


Which member of each pair would you expect to have the most downfield signal? a. CH3Clor C2H6; b. CCl3CH3 or CF3CH3; c. CH3R or CH2ClR; d. RC(O)CH3 or RCH3. HINT:R is, as usual, a non-electronegative/non-electropositive group typically containing C andH atoms.


What is the chemical shift of a -CH3 group next to a benzene ring? Given that, make arough prediction for the position of the signal from a -CH2 group attached to a benzenering. How about a -CH group? What method did you use to come to your conclusions?HINT: This kind of reasoning is critical. Think about what you need to do to get yourselfto be able to produce it.


Might a -CH2 group between a benzene ring and a -CH2Cl group appear deshielded? Why?


Table 3 contains some data on the chemical shift of the -CH3 group for compounds of thetype CH3E where E is given in the table and χ is the electronegativity of the atom of Eattached to the carbon. Do you see any relationships? HINT: Whenever a scientist is askedthat kind of question, she makes a plot, even if it is only crude.


2.135 19

2.128. NMR Environments

How many different environments do the hydrogen atoms have in each of the following?a. 1-chloropropane; b. 2-chloropropane; c. 2,3-dimethylbutane; d. 2,2-dichloropropane.HINT: Make sure that you consider free rotation.


Are all the hydrogen atoms in the same environment in 10? in 11? in 12? in 13?


How many different environments are there in the compounds of the last problem that don’thave only one environment?


How many 1H nmr signals will we see for each of the compounds 14-17? HINT: If you haveheard of it, ignore spin-spin coupling.


The 1H nmr spectrum of toluene shows a sharp peak at 2.28 δ and a broader peak at 7.1 δ.How many different peaks should be present in toluene (which is the trivial name for methyl-benzene)? Account for the observed spectrum. HINT: You might use the words “acciden-tally equivalent” in your answer.


Actively review your notes from the last lecture; don’t just read them. Summarize thepoints of discussion. Close your notes and repeat to yourself the summary. How are thepoints of discussion interconnected? Would you have connected them in the same way?

2.134. NMR and Chemical Shift

Predict the approximate position of the signal(s) in the 1H nmr spectrum for 2-butenal andfor methylbutyrate. HINT: Ignore spin-coupling.


2.143 20

2.135. NMR, Chemical Shift, and Integration

Predict the approximate position of the signal(s) in the 1H nmr spectrum for 2-methyl-2-propanol, 1-chloro-2,2-dimethylpropane, propene, and ethylchloride. It isn’t necessary, butif you want to be reasonably accurate use the nice tables at

http://www.chem.wisc.edu/areas/reich/handouts/nmr-h/hdata.htm .Give integrations. HINT: You should neglect spin-spin coupling in this problem.


Predict the approximate position of the signal(s) in the 1H nmr spectrum for compounds18-20. Give integrations. HINTS: (1) You may treat all of the hydrogen atoms in a benzenerings as equivalent for now. (2) You should neglect spin-spin coupling in this problem.


How would you distinguish between 21 and 22 using 1H nmr (ignoring spin-spin coupling)?


How would you, in principle, distinguish between 23 and 24 using 1H nmr (ignoring spin-spin coupling)?


How would you distinguish between 25 and 26 using 1H nmr (ignoring spin-spin coupling)?


Predict the approximate positions of the signals and their relative areas in the 1H nmrspectrum of CH3C(O)OCH3.


Predict the approximate positions of the signals and their relative areas in the 1H nmrspectrum of 2-bromobutane.


A compound of formula C2H6O has only one peak in the nmr spectrum. Give a structuralformula for this compound? HINT: Use ihd.


2.154 21


A compound of formula C3H6Cl2 has only one peak in the nmr spectrum. Give a structuralformula for this compound?


Find the number of 1H signals, predict their positions, and state their relative areas forcompounds 27-30. HINT: Treat all protons on the benzene ring as if they were “accidentallydegenerate.”


How many different chemical shifts would you expect in 1-chloro-3-fluoro-propane? Whichsignal is due to which hydrogen atoms? What are the relative areas? Ignore spin-coupling.


A compound of formula C4H9Br has three 1H nmr signals, one at about 1.0 δ (Area 3),a second at 2.0 δ (0.5) and a third at 3.3 δ (1). What is the compound? HINTS: (1) Ifyou have heard of spin-spin splitting, ignore it for this problem. (2) As always, if given aformula, use ihd.

2.147. NMR Areas*

In the last problem, articulate how you handled the relative areas given the total numberof hydrogen atoms in the molecule was 9.


A compound with the formula C7H14O has two 1H nmr signals. What is the compound?HINT: If you have heard of spin-spin coupling, ignore it.

2.149. NMR Complexity*

In the last problem, articulate what you can conclude from the relative simplicity of thenmr spectrum and the complicated formula–14 hydrogen atoms.


A compound with the formula C5H12O has 1H nmr signals at 3.2 δ (20) and 1.2 δ (59).What is the compound?

2.151. NMR Areas*

In the last problem, articulate how you handled area ratios that looked to be 6 to 2 whenyou had a total of not 8, but 12 protons.


A compound with the formula C9H10O2 has 1H nmr signals at 7.4 δ (108), 5.2 δ (45) and2.2 δ (66). What is the compound? HINTS: (1) Last time: As always when given a formula,use ihd. (2) Ignore spin-spin coupling and treat all protons on a benzene ring as if they arein one environment.

2.153. NMR and Reactions

How many 1H nmr signals will the product of the reaction of 3-pentanone with ethylmagne-sium Grignard have (after acidification) in the 1H nmr spectrum? HINT: Ignore spin-spincoupling.


2.161 22


How many 1H nmr signals will the product of the reaction of trans-2-butene with ozone,O3, followed by treatment with Zn, have in the 1H nmr spectrum? What will be theirapproximate positions? Ignore spin-spin coupling.


How many 1H nmr signals will the product of the reaction of trans-2-butene with H2 overPd(C) have in the 1H nmr spectrum? What will be their approximate positions? Ignorespin-spin coupliing.


Bromomethyl-methyl ether has an 1H nmr spectrum with signals at 5.7 δ (2) and 3.2 δ (3).Assign the peaks to hydrogen atoms in the structure.

2.157. NMR Analysis*

Look at your assignment in the last problem and think about it. Do this regularly with allnmr structures. It will serve you well in the future to have a good grasp on where signalsoccur. Oops, forgot to ask a question; this must be important.


1-Bromo-2-methylpropane has an 1H nmr spectrum with signals (ignoring spin-spin cou-pling) at 1.05 δ (6), 1.98 δ (1) and 3.3 δ (2). Assign the peaks to hydrogen atoms in thestructure; then see the last problem.


A compound of formula C7H14O has the following 1H nmr spectrum (with integration): 1.0δ (Area 18) 2.1 δ (6), and 2.3 δ (4). What is the compound?


Look at your assignment in the last problem and look how beautifully the data in Table 1allow you to easily solve it. Note that 0.2 δ difference (observed in the problem) betweenthe methylene group and the methyl group is exactly what it is in the table. Do you thinkTable 1 is useful?


2.172 23


A compound of formula C9H13N has the following 1H nmr spectrum (with integration): 2.25δ (3) 3.4 δ (1), and 7.3 δ (2.5). What is the compound? Be sure that you can account for thevalues of the various chemical shifts. HINT: You may need those “accidentally equivalent”words again.


Look at your assignment in the last problem. Why are the methylene protons deshielded?


Predict the approximate positions of the signals present in the 1H nmr spectrum of CH3C(O)CH3.HINT: Hear any bells?


How would you use chemical shift and integration to distinguish between HCCCH2OH andH2C−−CHC(O)H? HINT: Make sure you have the Lewis structures before you answer.


A compound with the formula C6H3Cl2(NO2) has an 1H nmr spectrum (with integration):7.63 δ (1) 8.09 δ (1), and 8.36 δ (1). What structures are not possible? HINTS: Thiscompound has a benzene ring; and the signals in that ring are not accidentally degenerate.(2) The problem ignores spin-spin coupling. (3) The formula implies that the compoundcontains an -NO2 group (isovalent with H) and not some other combination of N and O.

2.166. NMR and Equivalent Protons

How many 1H nmr signals in 31-33? HINTS: (1) If you think about the ring as being planar(it isn’t, but that works, as we will see), and consider hybridization for four- coordinatecarbons, you will find the first two molecules have a top and a bottom side. (2) This makesthe first two problems somewhat challenging.


Using chemical shift and integration data only, how would you distinguish between 34 and35?


In 1H nmr, where does the H atom in RC(O)OH absorb? HINT: “R” is some unspecifiedC,H group. HINT: There are two odd ball chemical shifts in 1H nmr; this is one of them.


In 1H nmr, where does the H atom in CH3C(O)R absorb?


In 1H nmr, where does the H atom on an alkene absorb?


In 1H nmr, where do the H atoms in benzene-R absorb?


2.183 24

2.172. NMR and Chemical Shift*

In 1H nmr, where does the H atom in CF3C(O)H absorb? As they say in Beebe, Arkansas,which is right down the road from Searcy, “There ain’t no more bells in 1H spectroscopy,”than those you have discussed in this and the previous four problems.

2.173. NMR and Spin-Spin Splitting

A -CH3 group has a neighboring C with one H atom. How many different spin orientationscan that single neighboring hydrogen atom take?

2.174. NMR and Spin-Spin Splitting*

Given your answer to the last problem, how many different magnetic fields can the -CH3

group that has one H atom on a neighboring carbon “see?” Into what kind of structure isthe signal of the -CH3 group split?


A -CH2- group has one H atom on a neighboring carbon atom. How is the -CH2- groupsplit?


Complete the following sentence: “To determine the splitting of the hydrogens on a givencarbon, you need to examine the . . . ”


A -CH3 group has two equivalent H atoms on a neighboring carbon atom. How manydifferent spin orientations can those two neighboring hydrogen have? List them pictorially.What is the relative probability of each of the possible orientations? Do any of the possibleorientations produce equivalent fields? How many different fields are possible? What is theprobability of each?

2.178. NMR and Spin-Spin Splitting*

A -CH3 group has two equivalent H atoms on a neighboring carbon atom. How will thesignal of the -CH3 group be split? What will be the relative areas of the components of thesignal?


A -CH2- group has three equivalent H atoms on a neighboring carbon atom. How is the-CH2- group split?


A -CH= group has two neighboring equivalent -CH3 groups. How is the CH group split?

2.181. NMR and a Spin-Spin Splitting Rule

From the last eight problems, show that the number of peaks into which a signal is split isgiven by the expression (n+1), where n is the number of neighboring hydrogen atoms.

2.182. NMR and Splitting Pattern

Predict the spin splitting of the peak due to the hydrogen atom on the methyl group ofCH3CH(Cl)2.


2.193 25


Predict the spin splitting of the peak due to the hydrogen atom on the methine group ofCH3CH(Cl)2.


Predict the spin splitting of the peak due to the hydrogen atom on the methyl group ofCH3CH2OH.


Predict the spin splitting of the peak due to the hydrogen atom on the methylene groupof CH3CH2OH. HINT: Ignore the hydrogen atom on the oxygen atom: Under normalcircumstances, rapid exchange wipes out any spin-spin coupling of this hydrogen atom.


Predict the spin splitting of the peak due to the hydrogen atom on C-2 of 34.


Predict the spin splitting of the hydrogen atoms of 36.


Predict the spin splitting of the peak due to the hydrogen atom on the methyl group of 35.


Here is a slightly harder spin-spin coupling problem. Predict the spin splitting of the peakdue to the hydrogen atom on C-2 of 35. Be careful; the fluorine atom has a spin of 1/2 butclearly is not equivalent to a hydrogen atom.

2.190. NMR Splitting Pattern

Predict the spin-spin splitting pattern (i.e., triplet at 1.5 δ, etc) for 1,1,2-tribromoethane.

2.191. Reciprocity of NMR Splitting Pattern

Imagine you have a -CH3 group next to a -CH2- group. From the point of view of the-CH3 group, how many neighbors does it have? What splitting will you see at the -CH3

group? From the point of view of the -CH2- group, how many neighbors does it have? Whatsplitting will you see at the -CH2- group? Since the two interactions are modulated by thesame electrons, they are completely reciprocal. If the -CH2- group “splits” the -CH3 group,the -CH3 group will “split” the -CH2- group. How will each be split?

2.192. Reciprocity of NMR Splitting Pattern*

Continuing with the scenario from the last problem, the magnitude of the splitting, almostalways called J, is eactly the same at both signals. If the -CH3 group is split into a tripletwith a separation between the peaks of J = 8.0 cps, what will be the separation of thevarious peaks in the -CH2- group?


2.199 26

2.193. NMR

A compound of formula C4H8O has three 1H nmr signals: 1.06 δ (triplet J=7.6, 3), (ding)2.14 δ (s, 3) (ding), and 2.45 δ (q, J=7.6, 2). What is the compound?

2.194. NMR and Learning Organic Chemistry

When you work on nmr problems, figure out something that you know and then pursue it.For instance, in the problem, “A compound of formula C4H8Br2 has two 1H nmr signals:1.97 δ (s, 6) and 3.89 δ (s, 2). What is the compound?” I could start with the signal at 3.89δ which is deshielded and hence must be next to one bromine atom and probably adjacentto another. Now to pursue: That same signal is a singlet so there is no hydrogen close tothe hydrogen(s) in the signal. We have:

where the squiggly lines are NOT to hydrogens, and one of them is probably to a bromine.I have taken advantage here that the integration of that signal is two, so it is a -CH2-group. You can pursue further to finish the problem.

2.195. Structure Assignment with NMR

A compound of formula C8H9Br has 1H nmr signals: 2.01 δ (d, 3), 5.14 δ (q, 1) and 7.35δ (broad s, maybe g, 5). What is the compound? HINTS: 1. Always use ihd and pursue.2.“g” means a mess as we will see if we haven’t yet; treat it as “no knowledge” for now.To start the pursuit (which could start in lots of different ways), I notice the ihd suggestsa benzene, and I find confirmation in the signal at 7.35 δ. Pursuing, I see the area is 5and that the total area is 9, which is consistent with the total number of hydrogen atoms.Therefore the benzene ring has only one substituent on it. You finish it.


A compound of the formula C5H10O2 has four 1H nmr signals: 1.14 δ (t, J=7.7, 3), 1.26 δ(t, J=7.2, 3), 2.32 δ (q, J=7.7, 2), and 4.13 δ (q, J=7.2, 2), What is the compound?


A compound of the formula C7H14O has 1H nmr signals: 1.06 δ (s, 6), 2.15 δ (s, 2), and2.33 δ (s, 1.4), What is the compound? HINT: Use the rule as modified in the last problem.


A compound of the formula C5H10O2 has two 1H nmr signals: 1.14 δ (s, 9), 11.49 δ (broadsinglet, exchangeable, 1), What is the compound? HINT: “Exchangeable” means a hydrogenatom that rapidly comes on and off the site of the organic molecule; it usually means a -OHor a -NH2.


2.206 27

2.199. Splitting from Multiple Sources, Case 1

Imagine a situation where a -CH2- has a methyl group on both sides. That can be (is ormust be,in this case) like having six hydrogen atoms on neighboring carbon atoms. Ourrule from problem 181 must be modified slightly in this case: it becomes (n+n’+1) wheren is the number of neighboring hydrogen atoms on one side and n’ is the number on theother. In this case it would be (3+3+1), and we would see a septet splitting pattern. Whatmight be the splitting of a -CH2- which had three hydrogen atom next to it on one side andone on the other side? HINT: The conditional “might,” “can be,” are because of a problemwe will get to.


A compound of the formula C7H14O has 1H nmr signals: 0.9 δ (t, 3), 1.1 δ (d, 6), 1.6 δ(sextet, 2), 2.42 δ (t, 2), and 2.6 δ (heptet, 1), What is the compound? HINT: Apply therule from the last problem.


Our (n+n’+1) rule, see problem 199, breaks down when the size of the coupling of the nhydrogen atoms is not the same as the splitting of the n’ hydrogen atoms and the chemicalshift difference is small. Under this circumstance, you get a multiplet (indicated by a “m”),a mess (also a “m”), or, as called by those less proficient in the language, garbage (indicatedby a “g”). You can learn little from the spin-spin coupling of such a peak except that itis coupled to two (or more) different hydrogen atoms. The following is an example: Acompound of the formula C5H10O2 has four 1H nmr signals: 0.99 δ (d, 6), 2.12 δ (m, 1),2.23 δ (d, 2), and 11.9 δ (broad singlet, exchangeable, 1), What is the compound? HINT:This is a beauty for pursuit. The 0.99 δ peak is a doublet; hence coupled to one hydrogenatom. Pursue! Where is that one hydrogen atom? It must be the 2.12 δ peak, as that isthe only one with an integration of 1. Pursue! The 2.12 δ peak is a multiplet, hence mustbe coupled to some other set of hydrogen atoms. Those others must be the 2.23 δ peak, asit is the only other peak that is split (and remember, if A splits B, B must split A). Youcontinue.


A compound of the formula C9H11Br has 1H nmr signals: 2.2 δ (quintet, 2), 2.75 δ (t, 2),3.35 δ (t, 2), and 7.2-7.5 δ (g, 5), What is the compound? HINT: Apply the rule from thelast problem.


A compound of the formula C9H8O2 has 1H nmr signals: 5.4 δ (d, 1, J=15), 7.2-7.5 δ (g,5), 7.8 δ (d, 1, J=15), and 12.4 δ (s, 1, exchanges with D2O), What is the compound?


You have two compounds with the formula C10H12O. The first has 1H nmr signals: 1.18 δ(t, 1.5), 2.4 δ (s, 1.5), 2.95 δ (q, 1), 7.24 δ (d, 1), and 7.8 δ (d, 1). The second has 1H nmrsignals: 1.31 δ (t, 3.1), 2.65 δ (s, 2.9), 2.75 δ (q, 2.0), 7.3 δ (d, 1.95), and 7.8 δ (d, 2.1).HINT: You will need to use Table 1 carefully to be successful in obtaining an answer.

2.205. Using NMR to Distinguish Isomers

How would you use 1H nmr to distinguish between 2,3-dimethylbutane and 2,2-dimethylbutane?Remember that integration is relative only, so it cannot be used absolutely.


2.216 28

2.206. Using NMR to Distinguish Molecules

How would you use 1H nmr to distinguish between diethylether and ethyl-methyl ether?Remember that integration is relative only, so it cannot be used absolutely.


How would you use 1H nmr to distinguish between 3,6-dimethyl-1,4-cyclohexadiene and1,3-dimethyl-1,4-cyclohexadiene? Remember that integration is relative only, so it cannotbe used absolutely.


How would you use 1H nmr to distinguish between 1-methylethanol (isopropanol) andpropanol? Remember that integration is relative only, so it cannot be used absolutely.


How would you use 1H nmr to distinguish between 1,2,3-trichloropropane and 1,1,1-trichloropropane?Remember that integration is relative only, so it cannot be used absolutely.

2.210. Using NMR to Distinguish Molecules

How would you use 1H nmr to distinguish between 2,2-dimethylbutane and 37? Rememberthat integration is relative only, so it cannot be used absolutely.


Problems 199 and 201 outline two situations where spin-spin coupling occurs from morethan one source. There is a third case. If the n hydrogen atoms on one side of the site onwhich we are focussed and the n’ hydrogen atoms on the other side have sufficiently differentJ values and the chemical shift is large enough, we then see an (n+1)(n’+1) pattern. Thatis, we see, for instance, a doublet of triplets. A (d of t) means you have three major peaks,each of which is a doublet. The (n+1)(n’+1) pattern often occurs when one of the couplingsis long range (more than three bonds away), which is rare. An example: A compound offormula C5H8 has 1H nmr signals: 1.00 δ (t, 3), 1.55 δ (sextet, 2), 1.94 δ (t, 1), and 2.15 δ(t of d, 2). What is the compound?

2.212. Prediction of NMR Spectrum

Predict the 1H nmr spectrum for 4,4’-dimethyl-1-pentyne. HINTS: (1) This compoundexhibits (n+1)(n’+1) peaks through the triple bond. (2) See problem 211.

2.213. Spectroscopic Identification

A compound of formula C4H8Br2 has IR, 2850-3000 cm−1 and a 1H nmr of 1.87 δ (s, 9.1),3.86 δ (s, 3.0). What is it?

2.214. Spectroscopy and Learning Organic Chemistry

A compound of formula C9H18O has IR, 1710 cm−1 and a 1H nmr of 1.2 δ. What is it?HINT: Here is my initial reaction for you to pursue. The IR suggests a carbonyl group andthe nmr suggests that the molecule is highly symmetrical–only one nmr signal. Take it fromthere. Pursue!

2.215. Spectroscopic Identifcation

A compound of formula C2H4Cl2 has IR, 2850-3000 cm−1 and a 1H nmr of 2.1 δ (d), 5.9 δ(q). What is it? HINT: Use ihd and pursue.


2.225 29

Table 4: 13C Chemical Shifts

Environment Chemical Shift, δ

Alkanes 0 to 60

Alkenes and Aromatics 100 to 170

Alkynes 60 to 90

Carbonyl

Not aldehydes or ketones 160-190

Aldehydes and ketones 190-220

All downfield with Electronegative substituents


A compound of formula C3H6Br2 has IR, 2850-3000 cm−1 and a 1H nmr of 2.4 δ (quintet),3.5 δ (t). What is it?

2.217. Spectroscopic Identificaton

A compound of formula C5H10O2 has IR, 1740 cm−1 and a 1H nmr of 1.15 δ (t, 3), 1.25 δ(t, 3), 2.3 δ (q, 2), and 4.32 δ (q, 2). What is it? HINT: The 1.15 δ (t, 3) signal must benext to one of the two signals with integration of 2. Pursue!


A compound of formula C6H14O has IR, 2850-3000 cm−1 and a broad band at 3200 cm−1.It has a 1H nmr of 0.8 δ (t, 6), 1.0 δ (s, 3), 1.5 δ (q, 4), and 1.6 δ (s, 1). What is it? HINT:The 0.8 δ signal must be next to the 1.5 δ signal, as they are the only things split. Pursue!


A compound of formula C6H14O has nothing of interest in the IR. The 1H nmr has peaksat 1.1 δ (d, 30) and 3.6 δ (heptet, 5). What is it?


A compound of formula C8H12O has a IR with prominent peaks at 1685 cm−1 (broad andstrong), 1625 cm−1 (sharp), 3105 cm−1, and 2950-3000 cm−1. The 1H nmr has a doublets at6.7 and 5.85 δ, both with integrations of 1, triplets at 1.87 and 2.47 δ, both with integrationsof 2, and a singlet at 1.16 δ with an integration of 6. Identify the compound.

2.221. 13C NMR

Predict the decoupled 13C nmr of ethanal.

2.222. 13C NMR

Predict the decoupled 13C nmr of 3-butene-2-one.

2.223. 13C NMR

Predict the decoupled 13C nmr of 2-butanol.

2.224. 13C NMR and Off Resonance Decoupling

Predict the position and splitting of the 13C nmr peaks in 2-butanol with off resonancedecoupling.


2.232 30

2.225. 13C NMR Spectroscopic Identification

A compound of the formula C4H8O has four 13C nmr signals: 7.87 δ (q), 29.43 δ (q),36.87 δ (t), and 209.28 δ (s) where the values in parenthesis are the off-resonance decoupledsplittings. What is the compound?


A compound of the formula C6H12 has 13C nmr signals at 17 δ, 25 δ, and 138 δ. What isthe compound?


A compound of the formula C7H7Br has seven decoupled 13C nmr signals: 21.05 δ, 122.31δ 127.65 δ, 128.48 δ, 129.70 δ 132.06 δ, and 140.07 δ. What are possible identifications ofthe compound?

2.228. Choice of Spectral Method

Which method(s), IR, mass spectroscopy, 1H nmr, or 13C nmr would you use to distinguishbetween 61 and 62? Explain your answer.






A compound has five 13C nmr peaks: 11.97 δ, (q), 25.90 δ, (t), 132.10 δ (d), 160.24 δ, (d)and 194.09 δ (d) [splitting patterns from off-resonance decoupling] and five 1H nmr peaks:1.13 δ (t, 3), 2.38 δ (quintet, 2), 6.12 δ (d of d, 1), 6.942 δ (d of t, 1), and 9.52 δ (d, 1).What is the compound?


2.239 31

2.232. Spectroscopic Identification and Learning Organic Chemistry

A compound has an IR with interesting peaks at 3082 and 3060 cm−1 as well as 1621 cm−1.The 1H nmr has peaks at 5.225, 5.737, 6.692, and between 7.1 and 7.5 δ. The first two aredoublets with an integration of 1, the third is a doublet of doublets with an integration of1, and the last is a mess (sometimes called garbage) with an integration of 5. The 13C nmrhas 6 peaks at 113.7, 126.2, 127.8, 128.5, 137.0, and 137.6 δ. What is the compound? Howdo we analyze this? The bunch of 1H nmr peaks in the region of 7.1 to 7.5 δ catch my eye.Likely a benzene ring. Pursue! Area is 5 which suggests a monosubstituted benzene ring.Pursue! That would mean that there are four kinds of carbon in the ring, accounting forfour of the 13C peaks. The two that are left (no matter which two you choose) are in theregion of sp2 hybrid carbon atoms, suggesting another double bond. Take it from there andpursue!


A compound with formula C4H8O2 has a 1H nmr with a broad singlet at 12.2 δ, a heptetat 2.6 δ, and a doublet at 1.21 δ. What is the compound?


A compound of formula C3H6O has IR, 1730 cm−1 and a 1H nmr of 1.11 δ (t), 2.46 δ (g)and 9.79 δ (t). What is it?


A compound of formula C5H8O2 has a 1H nmr with a triplet at 1.1 δ, a singlet at 2.32 δ,and a quartet at 2.78 δ. The relative integrations are 3, 3, and 2, respectively. What is thecompound?


A compound with a formula C7H12O2 has an IR band at 1746 cm−1 and 1H nmr peaks at1.8 δ (m, 2), 2.12 δ (d of t, 2), 2.41 δ (t, 2), 3.76 δ (s, 3), 4.9 δ (m, 2) and 5.68 δ (m, 1).The 13C nmr has peaks at 23, 34, 35 δ, all decoupled triplets, 51 δ (q), 115.9 δ (t), 137 δ(d), and 174.9 δ (s). What is the compound? The ihd is 2 and the 1746 cm−1 suggestsa carbonyl. Pursue. This is verified by the 174.9 peak, which further demands it has anadjacent oxygen (it is too low in the 13C spectrum for a ketone or aldehyde). Continuingto pursue. The only peak in the hydrogen spectrum that could be attached to that -O- ofthe -C(O)O- group is the 3.76 δ peak which is a methyl group. So we have a -C(O)COCH3.That ends that pursuit. On to another. The 137 and 115.9 δ peaks are an alkene, as arethose (I pursue) at 4.9 and 5.68 δ. The integration of the former indicates a terminal alkene.You can finish it.


A compound of the empirical formula C4H8O has three 1H nmr signals: 1.06 δ (d, 6); 2.39δ (garbage, 1), and 9.57 δ (d,1). What is the compound?


A compound has the formula C4H8O2; IR 1730 cm−1. The 1H nmr has peaks at 2.1 δ (s,31), 3.4 δ (s, 30), and 3.9 δ (s, 18.8). What is the compound?


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A compound with the empirical formula C4H8O2 has an 1H nmr spectrum: triplet at 1.27δ (1.0), singlet at 2.03 δ (1.05), quartet at 4.11 δ (0.68). What is the compound?


A compound of formula C9H12 has IR, 2850-3150 cm−1 and a 1H nmr of 1.25 δ (d, 6), 2.95δ (heptet, 1) and 7.3 δ (g, 5). What is it?


A compound with formula C4H8O has four 13C nmr peaks: 37.11 δ, (t), 61.61 δ, (t), 117.21δ (t), and 135.02 δ (d) [splitting patterns from off-resonance decoupling] and six 1H nmrpeaks: 2.318 δ (g, 2), 2.76 δ (broad, exchanges, 1), 3.65 δ (t, 2), 5.10 δ (d of d, 1), 5.13 δ(d of d, 1), and 5.82 δ (g, 1). What is the compound?


A compound with the formula C9H13N has an 1H nmr spectrum as follows: 2.25 δ (s, 6), 3.43δ, (s, 2), 7.32 δ, (g, 5). What is the compound? The ihd is 4. I would first guess, therefore,a benzene ring. Pursue. That is consistent with the signal at 7.32 δ, whose integration(pursuing) suggests a monosubstituted benzene ring. End of that pursuit. The signal at2.25 δ with integration of 6 suggests two methyl groups. Pursue. They are deshielded andhence probably on the N. You can take it from there.

2.243. Spectroscopc Identification

A compound with formula C7H14O has six 13C nmr peaks: 13.81 δ, 17.24 δ, 18.23 δ, 40.80δ, 42.26 δ and 214.77 δ [decoupled] and five 1H nmr peaks: 0.96 δ (t, 3), 1.09 δ (d, 6), 1.59δ (sextet, 2), 2.42 δ (t, 2), and 2.61 δ (heptet, 1). What is the compound?


A compound with formula C5H9N has four 13C nmr peaks: 21.79 δ (q), 25.98 δ, (d), 26.13δ (t), and 118.89 δ (s) [off-resonance decoupled] and three 1H nmr peaks: 1.07 δ (d, 6), 2.02δ (nonet, 1), and 2.23 δ (d, 2). What is the compound?


A compound with formula C6NO2ClH4 has an 1H nmr with two peaks, a doublet at 7.4 δand another doublet at 8.2 δ. What is the compound?


Make a list of the steps you would take to determine the identity of a compound given the1H nmr spectrum of the compound. Could you change the order of attack? How?

2.247. IR Review

How would you use IR to distinguish between cyclohexane and trans-2-hexene.

2.248. 1H NMR Review

How would you use 1H nmr to distinguish between cyclohexane and trans-2-hexene.

2.249. 13C NMR Review

How would you use 13C nmr to distinguish between cyclohexane and trans-2-hexene.


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2.250. Equivalent Hydrogen Atoms and 1H NMR

Find a structure for a nine carbon compound (with only hydrogen atoms in addition) whose1H nmr has two singlets.

2.251. Using Your Knowledge to Predict NMR Signal Structure

The proton nmr of CHD2I consists of a five line pattern with intensities 1:2:3:2:1. HINT:D has a spin of 1, which means the spin projection could be 1, 0, or -1 for each of the twoD. Justify this splitting of the proton spectrum.

2.252. Using Your Knowledge to Understand NMR Spectra

The 1H nmr of N,N-dimethylformamide has signals at 2.9 δ, 3.0 δ, and 8.0 δ. Explain.

2.253. Using Your Knowledge to Predict Chemical Shifts

The compound, 18-annulene, 39, has 1H nmr signals at 8.9 δ (s, 12) and -1.8 δ (s, 6).Explain. HINT: That really is a minus sign!


A compound with formula C6H14O has four 13C nmr peaks: 17.7 δ, 26.4 δ, 38.9 δ, and73.0 δ and four 1H nmr peaks: 0.90 δ (d, 6), 1.10 δ (s, 6), 1.25 δ (broad, disappears upontreatment with D2O), (s, 1), and 1.3 δ (heptet, 1). What is the compound?

2.255. Using Your Knowledge to Understand NMR Spectra

The proton nmr spectrum of 2,2,3,3-tetrachlorobutane is a function of temperature. Atroom temperature, it exhibits a single peak. At low temperatures, a pair of peaks, ratherclosely spaced, are found. Explain.

2.256. Review–Typical First Exam Questions

Give the zigzag line structure, and indicate the hybridization at each carbon atom, forpent-3-ene-2-one.

2.257. Review–Typical First Exam Questions*

Sketch or describe the highest occupied molecular orbital (HOMO) on the molecule of theprevious question.


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2.258. Review–Typical First Exam Questions**

Are there any other electron pairs in pent-3-ene-2-one that are relatively loosely held? Isso, how would you describe those electrons? HINT: For instance, σ electrons between C1

and C2.

2.259. Review–Typical First Exam Questions***

At what site (or sites) might a nucleophile such as H− attack pent-3-ene-2-one?


If we look at a benzene ring which lies in the x,y plane, what hybridization is used by acarbon atom in that molecule? Be specific in stating what orbitals are used in making thosehybrid orbitals? What orbital(s) is(are) not used for the hybrid orbitals?


Is a π bond stronger or weaker than a σ bond? Explain briefly. Draw something.


Make a drawing of the most stable conformer of 1-chloropropane?


Make a drawing of a less stable form of 1-chloropropane that could be isolated at lowtemperatures. HINT: I do NOT want a diagram of a material on the “top of an energymountain.”


Use epwa to illustrate the following reaction: BH–4 reacts with pentanal, followed by treat-

ment with H+.


Use epwa to illustrate the following reaction: A mole of ethyl Grignard with a mole of 40.


Use epwa to illustrate the following reaction: A mixture of 40 with excess 41, followed byH+.


How would you make 2-methyl-3-pentanol from compounds containing 3 carbon atoms (orfewer)? Use epwa to explain your reasoning.


A compound of formula C4H10O has an IR with peaks between 2800-3000 cm−1 and noother interesting peaks above 1500 cm−1. The 1H nmr has four peaks: 3.34 δ (t, 2), 3.33δ (s, 3), 1.59 δ (sextet, 2), and 0.93 δ (t, 3). What is the compound? HINT: For partialcredit you must given your reasoning.


A compound has a M+. of 121, an IR as given in Figure 4, a 13C nmr with peaks at 151 δ,129 δ, 117 δ, 113 δ, and 40.5 δ, and a 1H nmr with peaks at 2.89 δ (s, 1.7) and 6.6 to 7.4 δ(g, or m, 1.4). What is the compound? HINT: For partial credit you must given reasoning.


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2.276 36


A compound of formula C4H7ClO has an IR with peaks between 2800 and 3000 cm−1 andat 1720 cm−1. The 1H nmr has three peaks: 3.45 δ (t, 2), 3.07 δ (t, 2), and 2.14 δ (s, 3).What is the compound? HINT: For partial credit you must give your reasoning.


A compound has a mass spectrum with peaks at 120 and 122, intensities of 0.31 and 0.09,respectively, and an IR with peaks between 3000 and 2800 cm−1. The 13C nmr has peaksat 18 δ, 30 δ, 40 δ, and 75 δ, and the 1H nmr has peaks at 1.02 δ (d, 18.3), 1.54 δ (s, 17.9),and 1.89 δ (heptet (septet), 3.1). What is the compound? HINT: For partial credit youmust give reasoning.


What is the HOMO of C2H2ClBr3? HINT: I do NOT want you to do an m.o. diagram.Figure it out logically. This is an easy problem.


Use epwa to show how the reaction of propyl Grignard, 4, with 5 occurs. NOTE: Afterreaction, the solution is treated with acid solution.


Draw a line (or zig-zag) structure for a compound with an IR spectrum with a broad peakat 3340 cm−1 and a peak at 1710 cm−1. Then draw a line (or zig-zag) structure for acompound with an IR spectrum with a peak at 3230 cm−1, a weak peak at 2330 cm−1. anda peak at 1660 cm−1.

2.275. Review–Typical First Exam Questioins

For each of the following reactions, check the side that dominates at equilibrium (the side”to which the reaction occurs”).

CH–3 + HCCH = CH4 + HCC–

HF + OH– = F– + H2O

HI + NH–2 = I– + NH3

H2S + NH–2 = HS– + NH3

H2Se + AsH–2 = HSe– + AsH3


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Table 5: Data for problem 277

13C δ 1H δ Splitting Integration

15 1.2 d 0.7020 1.6 q 0.5030 2.2 s 0.7431 2.7 quintet 0.2458 3.8 t 0.51204 3.95 s (exchanges) 0.26

Table 6: Data for problem 278

13C δ 1H δ Splitting Integration

24 1.3 t 630 2.4 s 632 2.7 q 4135 7.0 d 4137 7.2 d 4139141204206


Here is a sequential series of reactions. Give the structure of the overall product of thereaction, that is, the compound at the end of step 5.1. Bromobenzene, C6H5Br is treated with Mg metal in ether.2. The product of step 1 is mixed with butanal.3. The product of step 2 is treated with H+ and the neutral compound isolated.4. The product of step 3 is reacted with PCC.5. The product of step 4 is reacted with methyl Grignard and then treated with acid.


A compound of formula C6H12O2 has the 1H and 13C spectra shown in Table 5. What isthe compound? HINT: For partial credit you must give reasoning. That doesn’t mean youhave to write paragraphs: ”A triplet, so this hydrogen has 7 neighbors . . . ” would do if itwasn’t nonsense.


A compound of has a mass spectrum with a molecular ion peak of 176. It has an IR peaksat 3101 cm−1, 1725 cm−1, and 1640 cm−1. The nmr data is given in the Table 6. What isthe compound? HINT: For partial credit you must give reasoning; and since you have lotsof data, there is a lot of reasoning to be given.


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Use epwa to show the reaction of ethyl Grignard, CH3CH2MgBr, with 6, followed by treat-ment with acid. HINT: We haven’t studied this reaction (yet), but you should be able tofigure out what happens from what you should know.

2.280. Spectral Identification

A compound has a M+. peak of 168. The IR has interesting peaks at 3050, 1700(strong),and 1620 cm−1. The 1H has peaks at 0.9 (d, J=8, 11.7) δ, 1.1(s, 18.1) δ, 1.48(nonet, J=8,1.95) δ, 2.3(d, J=8, 4.03) δ, 6.08 (d, J=18, 3.9) δ, and 6.9 (d, J=18, 4.01) δ. What is thecompound?


Chm 222 - Smith Collegerlinck/Chm222/sec/pset2.pdfChm 222 Spring 2016, Exercise Set 2 Mass...

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