1
Ian R. Gould
PRINTED FIRST NAME
Person on your LEFT (or Aisle)
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
CHEM 234
PRINTED LAST NAME
H/H ~1.0
Eclipsing
H/Me ~1.4
Me/Me ~2.6
Me/Me ~0.9
Et/Me ~0.95
i-Pr/Me ~1.1
t-Bu/Me ~2.7
Gauche
Me/Et ~2.9
Interaction Energies, kcal/mol
ASU ID or Posting ID
Person on your RIGHT (or Aisle)
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C NR2
RC CRR2C CR2
Aromatic
CR OHO
C X
R NH2R OH
aminealcohol
3Y > 2Y > 1Y
020406080100120140160180200220
–H2C X
–H2C NR2
–OCH2–
01234567891011
C CHC HO
CR OHO
Aromatic Ar HAlkylmainly 8 - 6.5
C CH2
C CH3
O
3Y > 2Y > 1YAlkyl–OCH2–
CO
(δ, ppm)
variable and condition dependent, ca. 2 - 6 δ
R C N
O H C N
CN
CC
H
C ON H
C H
C N
O
HCO
CH
C CH
COR
ON H
C H
CO
O H
C O HO
CNR2
O
3000–3100
2850–2960
3300
broad ~3300
broad with spikes ~3300
2200
broad ~30001710
2200
1650
2720–28202 peaks
1735
1600–1660
1680
range of valuesbroad peak
small range usuallystrong
1600
CH
CH
C CHH
CH
CH
CH
CH
H
H
H
H
Approximate Coupling Constants, J (Hz), for
1H NMR Spectra
~7
~10
~2
~15~2
~8
Infrared Correlation Chart
NMR Correlation Charts
3000 200025003500 1500(cm-1)
THIS IS A CHM 234PRACTICE EXAM
MIDTERM #2PRACTICE TEST #1
the exam cover sheets look kind of like this
2
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 2 - NAMEQuestion 1 Give the IUPAC name for the following compounds. Be sure to use cis/trans, E/Z or R/S where appropriate.
OCH2CH2CH3
(3R)-propoxycyclopentene1 2
3
5 4H
Question 5 Sodium borohydride (NaBH4) reduces only aldehydes and ketones. Lithium aluminum hydride (LiAlH4) will reduce aldehydes and ketones and also esters and carboxlic acids. Give a BRIEF explanation for the different reactivities of NaBH4 and LiAlH4. Include the term "Lewis base" in your explanation.
LiAlH4 is more reactive than NaBH4 because the electrons in the Al-H bonds are higher in energy than those in the B-H bond, since Al is larger than B. LiAlH4 is thus the stronger Lewis base, its reactive electrons are higher in energy
Question 4.a) Give the organic reactant and the Grignard reagent you would use to make the bond indicated by the dashed line in the provided structure (do not include the aqueous acid workup step, stereochemistry is ignored in this question)
HO
Ph
O+Ph MgBr
c) Explain why the Grignard reaction shown would NOT work
Ph
HO
XO+Ph MgBr
the Grignard would have to attack the MOST substituted side of the epoxide, which is slower than attacking the least substituted side
b) Give the organic reactant and the Grignard reagent you would use to make the bond indicated by the dashed line in the provided structure (do not include the aqueous acid workup step, stereochemistry is ignored in this question)
HO
Ph
O
+Me MgBr
Ph
3
Question 5 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement3) Briefly explain whether the a solution of the product would be optically active or not4) Pay attention to stereochemistry including racemic mixtures unless specified
b)
a)
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 3 - NAME
d)
c)
O
CN
CNO
CNCN
heat+addition, achiral reactants, meso
product formed, not optically active
Na+ –OCH3
CH3OH
O OH
OCH3
addition, chiral reactants, single
enantiomer formed, optically active
HH
–OCH3
SN2
the expected Walden inversion occurs "pushes" the Me and H up
NBS, hνBr substitution, achiral
reactants, achiral product, not
optically active
1. Hg(OAc)2, CH3OHCH3
2. NaBH4
CH3
OCH3
neitheradditionnot opically active, achiral
Question 6. Provide the missing reactants for the following Diels-Alder reaction.
CNCN+ (±)
heat
4
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1- 4 - NAME
Δ
1) draw the arrow-pushing that describes formation of the PROVIDED product2) How many electrons are involved in the reaction?3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the ring closing be disrotatory or conrotatory?4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the transition state be Hückel or Möbius?5) Is PROVIDED PRODUCT allowed or forbidden and why?
6 electrons
Möbius
Forbidden, the allowed product of a 6-electron electrocyclic ring closing reaction would proceed via an aromatic Huckel transition state and would be disrotatory, not Mobius/conrotatory
Conrotatory
Question 5. The purpose of this question is to determine whether the provided product is allowed or forbidden
Question 6) For the following ion, draw all reasonable resonance contributors, draw an "actual" structure that includes partial bonds and partial charges (use δ to indicate partial charges), and draw the HOMO and LUMOs on TOP of the provided structures
the pi-molecular orbitals extend over the conjugated part of the structures and does not include any sp3 hybridized atoms
HOMOand
resonance
δδ
LUMO
"actual" structure
Question 7. Show how you would synthesize the target compond on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
Br
ONBS/hν
NaOMe
1. NaH2. PrBr
OH
1. BH3.THF2. –OH/H2O2
(±)
(±)
5
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 5 - NAME
Question 8) Explain why the products of the following reaction are an alcohol and a bromide, rather than two bromides, Draw a mechanism to support your reasoning
O OH Br+
HBrH Br
O
H Br
LA/BA
LB/BB
LB
LAthese are the final products
OH Br+
H BrLA/BA
LB/BB
OH2can't do a substitution at an sp2 hybridized
carbon via either SN1 or SN2, the
only possible further reaction is loss of
proton to reform the alcohol
X
SN2
NC
CN+
H2C CH2N
NC CN
Δ (±)
4(s) + 2(s) suprafacial/suprafacial allowed
* *
LUMOHOMO NC
CN
1 node
H2CN
CH2
CH3CH3
Question 9). Give the curved arrow-pushing and the ALLOWED product of the following cycloaddition reaction
H2CN
CH2
CH3
1 node
b) Give a pictorial representation of the wavefunction of the HOMO ON TOP OF THE STRUCTURE below for A, indicate the number and positions of any vertical nodes (ignore horizontal nodes)
c) Give a pictorial representation of the wavefunction of the LUMO ON TOP OF THE STRUCTURE below for B, indicate the number and positions of any vertical nodes (ignore horizontal nodes)
A
B
the ALLOWED product of the reaction must have two bonding interactions in the transition state, consideration of the wavefunctions of the HOMO and the LUMO indicates that suprafacial/suprafacial reaction is allowed, thus the 2 -CN groups start trans- and are also trans- in the product
d) Give a brief justification for the stereochemistry in your allowed product, you must include the following terms in your justification: suprafacial and/or antarafacial, HOMO, LUMO, bonding and/or anti-bonding
6
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2 - 2 - NAME
Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate.
START OF PRACTICE TEST #2
b) HOO
12
3 45
6 4-methoxy-3-methylhex-(3Z)-en-1-ol
(alcohol highest priority functional group, determines numbering)
ethers are alway just "alkoxy" substituents
a)Et
NO2
Br
1-bromo-2-ethyl-4-nitrobenzene
OHHBr
MeOH (solvent)OMe
OH2OMe
H OH
Me
O
Me
H
LBLA
LB/BB
LA/BA
LA/BA
LB/BB
HO
MeH
when dissolved in MeOH, HBr is essentially completely dissociated, just the same as it is in H2O
Question 2. Give a complete curved arrow pushing mechanism, and...1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they are also Brønsted acids/bases (LA/BA, LB,BB)2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM
4 steps
7
Question 3 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement3) Briefly explain whether the a solution of the product would be optically active or not4) Pay attention to stereochemistry including racemic mixtures unless specified
b)
a)
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2 - 3 - NAME
d)
c)
+CF3
heatF3C
(±)
addition, achiral reactants, racemic mixture, not
optically active(this is about as tricky a
Diels-Alder reaction I can come up with!)
OH
OH
1. MCPBA
2. H3O+
oxidationnot optically active, racemic mixture formed(±)
Br
1 Equiv. Na+ –CN
CNsubstitution, chiral reactants, single
enantiomer formed, optically active
Br BrSN2 at allylic,
specifially benzylic carbon is fast
O Na+ –OEt/EtOHOH
OEt
H H addition, chiral reactants, single
enantiomer formed, optically active
not protonated, attack least
substituted side
Δ
1) draw the arrow-pushing that describes formation of the product2) How many electrons are involved in the reaction?3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the ring opening be disrotatory or conrotatory?4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the transition state be Hückel or Möbius?5) Is THE REACTION SHOWN allowed or forbidden, and why?
4 electrons
Hückel
Forbidden, the allowed product of a 4-electron electrocyclic ring opening reaction would proceed via a Mobius transition state and would be conrotatory, not Huckel and disrotatory
NCH3
CF3F3C
H H NCH3
HH
F3C CF3
Disrotatory
Question 4) The purpose of this question is to determine whether the provided product is allowed or forbidden
8
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2- 4 - NAME
CN
CNCN
CN
+(±)
Question 4. Provide the missing reactants for the following Diels-Alder reaction.
N N N N NN
Question 5. For the following structure:a) Draw all additional reasonable resonance contributortsb) Draw on TOP of the structure a pictorial representatrion of the wavefunction of both the HOMO and the LUMO, give the number of vertical node (only) and indicate their positions.
N N
resonance contributors
HOMO
6 electrons in the π-system
2 vertical nodes
node node
N N
LUMO3 vertical nodes
node nodenode
Question 6. Rank the following structures in order of increasing rate of reaction in a Diels-Alder reaction with fumaronitrile (shown), and give a brief explanation that includes the terms "donating group", "withdrawing group", "energy of the electrons", "HOMO".
O
––– ––– –––< < CAB
the dienes differ by the substituents that are circled, the energy of the electrons in the diene, specifically those in the HOMO, are raised by donating groups and lowered by withdrawing groups, raising the energy of the electrons in the HOMO decreases the HOMO/LUMO gap (the LUMO on the fimaronitrile), which decreases the reaction activation energy and increases the rate
C has a strong donating group (non-bonding electrons on N) and a weak donating group (the alkyl chain), it reacts fastestA has a withdrawing and a strong donating group (non-bonding electron on the nitrogen), it is intermediateB has a withdrawing and only a weak donating group (the alkyl chain), it is slowest
NH
NH
ONH
A B C
withdrawing
strong donating weak donating
strong donatingwithdrawing
weak donating
CN
NCfumaronitrile
9
Question 7. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #2 - 5 - NAME
NBS, hν
Ph Ph
Ph PhBr
Ph Ph
t-BuO–+K
Ph Ph
OH
1. BH3.THF
2. H2O2/ –OH
Ph Ph
O– +Na
Ph Ph
O
Br
Na H
CN
NC+
H3CO H3COCN
CN(±)
H3COCN
CN(±)OR..
heat
Question 7 (20 pts.)a) Give the curved arrow-pushing and the ALLOWED product of the following cycloaddition. State whether the product is achiral, a mso compound, a pure enntiomer or a racemic mixture
A B
b) Draw the HOMO for reactant A and the LUMO for reactant B on top of the structures below, understanding that it may not be possible to get the geometry of the orbitals with respect to the structures exactly correct because the structures have to be drawn flat on the paper
HOMO LUMO
c) does the allowed reaction proceed suprafacial/suprafacial or suprafacial/antarafacial?suprafacial/suprafacial
H3COCN
NC
10
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #3 - 2 - NAME
Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate.
START OF PRACTICE TEST #3
OH1 2
3 4 56
7
(6R)ethoxyhept-(2Z)-en-4-yn-2-ol
*OEt
O
HCl cat.
OH
O
H
OH OHO
H
OHOLA/BA
LA
LB
LB/BB
LA/BA
H Cl
LB/BB
when dissolved in i-PrOH, HCl will be partially dissociated, an so it is not obvious which acid species, HCl itself or protonated alcohol will be responsible for
protonation of the epoxide, you can use either, however, the i-PrOH solvent will be present at MUCH higher concentrations than the conjugaye base anion from HCl, and therefore deprotonation occurs to i-PrOH (even if the proton eventually gets
returned to form HCl)
Question 2. Give a complete curved arrow pushing mechanism, and...1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they are also Brønsted acids/bases (LA/BA, LB,BB)2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM
OH
11
Question 4 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified3) State whether a solution of the product(s) would be optically active or not and give a brief explanation
b)
a)
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3 - 3 - NAME
c)
1 Equiv. HBr Br
(±)
achiral reactants, racemic product,
not optically active
reaction at THIS alkene fastest because the primary intermediate is a 3° cation
heatCO2CH3
CO2CH3
CO2Me
CO2Me
+
achiral reactants, meso product, not optically active must rotate to s-cis before reaction
=CO2Me
CO2Mesame
as
O Na+ –OEtEtOH (solvent)
EtO
OH achiral reactants, achiral product
formed, not optically active
epoxide NOT protonated, attack least substituted side
DCl
D
(±)(thermodynamic control conditions)
achiral reactants, racemic mixture,
not optically activeD = deuterium = "labelled hydrogen"
Cl
ClD deuteriate here first, makes most stable intermdiate
d)
Question 5) Indicate which reaction is more exothermic, give an explanation
A B
BrBrBr
Br
the two alkene products are structural isomers, when comparing structural isomeric alkenes the more substituted isomer is the more stable (Sayetzeff/Zaitzeff etc.) rule, formation of the more stable isomer is more exothermic, reaction B is more exothermic than reaction A
only 1 H atom on the C=C bond, 3 substituents, this alkene is more
substituted,more stable
3 H atoms on the C=C bond, 1 substituent, this alkene is less substituted, less stable
HH
HH
12
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3- 4 - NAME
Question 5. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
NBS, hν
Br
t-BuO–+K
O
O
O
O
O
O
H
H
O
O
O
H
H
HO
1. Hg(OAc)2/H2O2. NaBH4
Δ
ignore stereochemistry here
meso compound
S Δ
Question 6) The ylide below undergoes an electrocyclic ring closure reaction
t-Bu
a) give the curved arrow-pushing that accounts for product formationb) draw the product, paying special attention to relative stereochemistry of any substituentsc) indicate the locations of any chiral (asymmetric) carbons atoms with the symbol, and state whether it is racemic, a meso compound or achirald) give the NUMBER of electrons involved in the reactione) state whether the allowed reaction proceeds via a Huckel or a Mobius transition statef) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing
g) Draw a pictorial representation of the HOMO on top of the structure below, give the number of vertical nodes (only) and oindicate their positions
t-Bu
conrotatory
*S t-But-Bu
*H H
*
Mobius4
*
S
t-Bu
t-Bu1 node
13
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3 - 5 - NAME
Br CH3OH
OCH3H
O CH3
H
O HH3C
OH
H3C
OCH3
H
H3COOCH3
kineticthermodynamic
O CH3
H
Question 7. a) Give a full curved-arrow pushing mechanism for formation of both products of the provided reaction. One of these products would be formed preferentially under conditions of kinetic control, the other preferentially under conditions of thermodynamic control, indicate which is which. Indicate the Lewis acid and base at each step and whether they are also Bronsted acids/bases.
b) Give a reaction energy diagram for both reactions in the SAME DIAGRAM
reaction coordinate
energy
Brboth
‡‡
‡
‡
‡ OCH3
H3CO
O HH3C
OH
H3C
CH3OH
kinetic
thermodynamic
kinetic
thermodynamic
heat
LB/BB
LA/BA
LA/BA
c) Give a brief explanation of how temperature is related to kinetic and thermodynamic controlat all temperatures the kinetic product is formed faster, at lower temperatures the reactions will be more IRREVERSIBLE, the kinetic product product will predominate, at higher temperatures the reactions will become more REVERSIBLE and the lower energy thermodynamic product can be formed and will start to accumulate
LB/BB
+A B
14
CHEMISTRY 234, MIDTERM #3 PRACTICE TEST #3 - 6 - NAME
Δ
CN
+
suprafacial/antarafacial
NC
CN
CN(±)
Question 8. The purpose of this question is to determine whether the provided product of the cycloaddition reaction given below is allowed or forbidden (there are several possible products of this reaction, we will focus our attention on this one to see if it is allowed)
a) give the curved arrow-pushing that accounts for product formationb) draw the HOMO and LUMO ON TOP OF THE structures as indicated above, and give the number of vertical nodes and clearly indicate their positionsc) IGNORING THE PROVIDED product for now, use the information from the F.M.O.s to decide whether the ALLOWED reaction would be suprafacial/suprafacial or suprafacial/ antarafacialyour answer________________________________d) Using the sterochemistry of the PROVIDED PRODUCT, decide state whether the it was formed via suprafacial/suprafacial or suprafacial/ antarafacial cycloadditionyour answer________________________________d) state whether the PROVIDED PRODUCT is allowed or forbidden, and give a BRIEF explanation that mentions the frontier molecular orbitals.
HOMO
LUMO
suprafacial/antarafacial
The provided product is ALLOWED, it is formed in suprafacial/antarafacial reaction and the phases of the HOMO and LUMO at the relevant carbons result in two bonding interactions for such a reaction
1 node
1 node1 node
non-aromatic
sp3
anti-aromatic4 electrons 4 electrons
anti-aromatic
8 electronsN
anti-aromatic
8 electrons
these electrons are in sp2 hybrid A.O.
Question 9) Classify the following structures as aromatic, non-aromatic or anti-aromatic, assume all structures are as flat as possible, AND give the number of electrons involved in the conjugated system
suprafacial on this reactant (shown with both bonds being made to the bottom of the carbon atoms)
antarafacial on this reactant (shown with one bond being made to the top of one carbon atom and one bond being made to the bottom of the other carbon atom)
CIS-
TRANS
the reaction is antarafacial on the lower reactant because the cis-stereochemistry of the substituents becomes trans- in the product (this would not be included as part of the answer)
15
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 2 - NAMESTART OF PRACTICE TEST #4
OMe
Me
Me
Me
OH
Me
Me
H
OH
H
H
H
Oi-Pr
i-Pr
i-Pr
i-Pr
––– ––– ––– –––< < <D A B C
Question 2) Rank the following in order of icreasing rate of reaction in a base catalyzed hydrolysis reaction (addition of water in the presence of hydroxide) and give a brief explanation (hint, think abouyt the slowest, rate determining step for base catalyzed hydrolysis)
A B C D
The rate determining step is hydroxide as Lewis base in SN2 type attack on carbon of the Lewis acid epoxide. This process is subject to steric hinderance, hence the order given.
OHOH OH OH
slow slowestfastestslowish!!
Question 1. Provide TWO Grignard reactions, A and B, that can be used to make the provided target structure. Give the organic reactant and the Grignard reagent that would be used, you do not need to specify the aqueous acid workup step, but you musty specify which of the C-C bonds is being made in the provided target structure.
OH
H
OMgBr+
H
O
BrMg+
OH
OHO
CH3BrMg+
A)
B)
OR...
Question 3 Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
CH3 CH2OH CH2 CH2OHCH2CH3
CH3 CH2Br CH3 CH2MgBr
O1.
2. H3O+
Mg.THF
PBr3
16
Question 4. For each reaction.1) Provide the missing reagents/conditions or major organic products as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified
b)
a)
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 3 - NAME
1. MCPBA
2. MeOH/HCl (cat.)
(ignore stereochemistry)
OH
OMe
+H3C CN
heatH3C
CN
(±)
+heat
For BOTH of the reactants A and B:b) Give a pictorial representation of the requested frontier molecular orbital as requested on top of the provided structurec) Give the number of electrons in the conjugated system that are relevant to the reactiond) State whether the allowed reaction is suprafacial or antarafacial
CNO
CH3
CC
CH3
H3C
H
H NO
H3C
CH3
Question 5) a) Give the curved arrow pushing and the product of the following reaction. Pay attention to stereochemistry and state whether a solution of the product(s) would be opticlly active or not.
A BCH3
(±)racemic mixture
formed, not optically active
CNO CH3
4 electronsCC
CH3
H3C H
H
A: HOMO
suprafacial 2 electrons
B: LUMO
suprafacial
not a racemic mixture, meso
compound
c)
d)1. MCPBA
2. H2O/HCl(cat.)
HO
OH
EtMgBrBr
17
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4- 4 - NAME
NBS/hν
Br
MgBr
Mg.THF
O
H
O1.
2. H3O+
OH
(ignore stereochemistry)
1. NaH2. PrBr
Question 6. Show how you would synthesize the target compound on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
essentially same as non-bonding
Question 7. Consider the energy of an electron in each of the following π-molecular orbitals AND a p atomic orbital on a carbon atom and rank them in order of increasing energy. Two of the energies will be essentially equal, as indicated below
A
B D
D
C
–––<
E
F (p atomic orbital)
A–––< C––– F–––< E–––< B–––lowestenergy
highestenergy
~
most bonding interactionsmost anti-bonding interactions
non-bonding by definition
roughlythe
same
18
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 5 - NAME
Question 8) Rank the following reactions, A, B and C, in order of INCREASING exothermicity. Give a BRIEF explanation
2 H2A
B2 H2
C
lowestexothermicity
highestexothermicity
< < BA C
the products are all the same, the energies at the end of all reactions is thus the same, the difference is in the reactants. A and C are conjugated, electrons are lower in energy, the reactants in A and C start lower in energy, thus less exothermic than B, the diene is more substituted in A compared to C, diene A is thus more stable, lower in energy, reaction A is least exothermic
2 H2
Δ
Question 9) The structure below undergoes an electrocyclic ring opening reaction (remember, D means deuterium, an isotope of hydrogen that is often used as a labelled hydrogen atom)
a) give the curved arrow-pushing that accounts for product formationb) draw the product, paying special attention to relative stereochemistry of any substituentsc) give the NUMBER of electrons involved in the reactiond) state whether the allowed reaction proceeds via a Huckel or a Mobius transition statee) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing
disrotatory
Huckel6
D
D
D
D
CN+
heat
CN(±)
Question 10. Provide the missing reactants for the following Diels-Alder reaction.
19
CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 6 - NAMEQuestion 12) Provide a detailed (arrow pushing) mechanisms for the following transformations. draw all important resonance structures. For each intermolecular step, identify the Lewis acid and base (LA/LB) as appropriate, and whether they are also Bronsted acids/bases (BA/BB), give the number of steps in your mechanism (hint BOTH SN1 and SN2 can occur at allylic carbon atoms)
H Br
conc. HBrO Ph
O PhH
heat
OH
Ph+
Ph
Br
OH + PhBrLB/BB LA/BA
LA
LB
OH
Ph
O
Ph OH
Ph
O– +Na
Ph
O
PhPCC/CH2Cl2
1. EtMgBr2. H3O+
NaH
Br
the last 2 stepscan also be shown as one reaction
with the 1. 2. notation
Question 13. Show how you would synthesize the target compond on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
this problem is slightly tricky, substitution here is SN1, the choice between SN1 and SN2 in simpler cases is the usual one, you can't do SN2 on a tertiary carbon and you can't do SN1 on a primary carbon, secondary is always a bit ambiguous, as is allylic, because both SN2 and SN1 are favored at this positions, HOWEVER, this is a mechanism problem, and in this case I gave you the product and you can see that the substitution can't have been Sn2 because the -Br is not on the original carbon that had the leaving group, so in this case it had to be SN1
a)
Br MgBr OH
OH
Mg.THF 1.
2. H3O+
O
Na2Cr2O7/H2SO4/H2O
OBr2/hν
b)
20
Question 6. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.
c) OH
Br
MgBr
OH
O
Mg.THF
PBr3
PCC
1.
2. H3O+
O
H Ph
a)PCC/CH2Cl2
1. MeMgBr2. H3O+
OH
O
OH
b)MCPBA
1. PhMgBr2. H3O+
OPh
OH
Question 3. For each reaction.1) Provide the missing reagents/conditions or major organicproducts as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified
b)
a)
c)
1.MgBr (±)O
Ph
2. H3O+ OH
O
O
1. Excess CH3MgBr
2. H3O+
OH
OH
OH 1. PBr32. Mg.THF3. D2O
D
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