Exp. 13*:

Exp. 13*:

CALCULATION, CHROMATOGRAPHIC,

AND SPECTRAL

APPLICATIONS

Objectives: To review common laboratory

calculations, chromatographic, and IR spectral techniques.

To learn to calculate efficiency of synthetic methods, and determine overall marketability of synthetic products.

To learn to use mass spectrometry and NMR spectroscopy for future use in structure elucidation.

PROPOSED CHEMICAL EQUATION

OH

H2SO4(cat)

2-methyl-2-pentanolMW: 102.17 g/mol

d: 0.835 g/mLcost: $67.20/12 mL

Amount used: 2.0 mL

sulfuric acidcost: $25.00/500 mL

Amount used: 0.5 mL

2-methyl-1-penteneMW: 84.16 g/mol

d: 0.682 g/mLcost: $129.50/25 mL

Product mass: 1.20 g

REACTANT

CATALYSTPRODUCT

Dehydration of 2-methyl-2-pentanol

LIMITING REAGENT & THEORETICAL YIELD

Mass RCT Moles RCT (using MWrct) Moles RCT Moles PROD (using stoichiometry) Moles PROD Mass PROD (using MWprod) Determine limiting reagent. Theoretical yield is always in the units of GRAMS

of PRODUCT! Theoretical yield =

# g REACTANT 1 mol of REACTANT 1 mol PRODUCT # g # g 1 mol REACTANT 1 mol PRODUCT

Amount you

started with

Molecular weight of starting material

Stoichiometric ratio Molecular weight of product

PERCENT YIELD

Percent yield = ACTUAL PRODUCT MASS (g) X 100 THEORETICAL YIELD (g)

Theoretical yield and percent yield

CALCULATIONSTheoretical Yield (g) based on alcohol Percent Yield

Theoretical Yield (g)

Actual Yield (g)Percent Yield

Show these calculations in your lab notebook!

Complete this table electronically and copy/paste into your final lab report!

GREEN CHEMISTRY CALCULATIONS

Green chemistry calculations are used to determine how “environmentally friendly” your choice of reagents, solvents, and conditions were.

This includes ATOM ECONOMY, EXPERIMENTAL ATOM ECONOMY, AND “Eproduct”.

ATOM ECONOMY Atom economy : based on the

efficiency of reactant atoms converted to product atoms.

Q: Were ALL of the reactant atoms converted to product atoms? Any atoms of the reactants that did NOT

appear in the product structure were converted to side products or waste.

Sometimes the side products and waste generated is harmful to the environment.

An experiment should be designed to minimize the generation of waste and unnecessary side products.

ATOM ECONOMY

Atom economy = MW desired product * 100 S MW reactants

• Atom economy is based on which reactants were selected to make the product.

• It assumes that the reactants were used in equivalent amounts, meaning that no excesses of any reactant were used.

• The closer the atom economy is to 100%, the better!

EXPERIMENTAL ATOM ECONOMY

Experimental atom economy = theoretical yield of product (g) * 100

S mass reactants

Q: Did we use ONLY the amount necessary to generate the product?• Sometimes an excess of one reactant is used

in order to drive the reaction to completion. For this reason, the experimental atom economy is calculated.

• Experimental atom economy is a more precise measure of efficiency than the atom economy—it takes into account the mass of each reactant used.

“EPRODUCT “

“Eproduct” = (% yield X % experimental atom economy)

100• “Eproduct” is the ultimate measure of efficiency, since both the conditions used and the amount of product that resulted under those conditions is taken into account.

• “Eproduct” is a number, not a percentage!

• The higher “Eproduct” is, the better!

IMPROVING EFFICIENCY… An efficient reaction would have

100% Atom Economy and 100% Experimental Atom Economy.

One could improve the efficiency of a reaction by adjusting the conditions of a reaction in an effort to improve either of these values, such as: Use different reactants to form the product

(AE) Use different amounts of reactants to form

the product (EAE).

COST ANALYSIS…Cost per synthesis

In order to calculate the cost of your synthesis, you must first determine the cost of the amount of each chemical used, including reactants, solvents, and catalysts!

Cost of solid ($) = Mass (g) of SOLID “A” used

*This calculation is performed for each solid used during course of synthesis!

Cost of liquid ($) = Volume (mL) of LIQUID “B” used

*This calculation is performed for each liquid used during course of synthesis!

Cost per synthesis ($) = Cost of “A” + Cost of “B”…etc.

Now that the cost per synthesis has been determined, based on the amount of product generated…

COST ANALYSIS…Cost per gram

Cost per gram ($/g) = cost per synthesis ($)

actual yield (g)

COST ANALYSIS…Cost per bottle

Now that the cost per gram has been determined, when compared to the manufacturers cost, how marketable is your product?Cost per bottle ($/g) = cost per gram x desired

bottle size

(*Can also be calculated in mL)

Green Chemistry Calculations

CALCULATIONS

Atom Economy (%) Experimental Atom Economy (%)

“E” product Cost per Synthesis ($)

Cost per Gram ($/g) Cost per 25 mL bottle

Atom Economy (%)Experimental Atom Economy (%)“E” productCost per Synthesis ($)Cost per Gram ($/g)Cost per 25 mL bottle

HPLC and TLC Chromatography

Introduced in Experiments 4 and 5. Difference between ANALYTE POLARITY and

SOLVENT POLARITY. UV detector is used in both. In order to be

detected, compounds must be UV active. Most solvents used in TLC and HPLC are not

UV active, therefore do not appear on the TLC plate or in the HPLC chromatogram!

GC Chromatography Introduced in Experiment 2.

ADJUSTED AREA % must be calculated to eliminate solvent quantity!

All chromatograms and spectra are available in folder on course website!

IR SPECTROSCOPY Introduced in Experiment 10.

Base values are given in correlation tables. Actual values are reported from actual

spectrum Don’t ever mention sp3 CH when using IR

spectroscopy to differentiate between reactants and products! They are too common!

EXAMPLE OF IR SPECTROSCOPY

OH

CH3

CH3

OH

CH3

CH3

THINGS TO CONSIDER…• What kinds of bonds

are present?• If they appeared in

the IR spectrum, where would they be?

• Now, look at the spectrum. Are they there?

Actual spectra are available in folder on course website!

IR SPECTROSCOPY BASE VALUES

Base values for Absorptions of Bonds (cm-1)O-H 3200-3600C-O 1000-1300

***(Esters have two!)***

C-H (sp2) 3000-3100C-H (sp3) 2800-3000

Aldehyde C-H 2700 & 2800 ***(there are two!)***

C=O 1650-1740***(location depends on functional

group!)***

C-X 500-700

MELTING POINT ANALYSIS Introduced in Experiment 7.

Detects all impurities! Recorded as Ti-Tf range.

Pure = matches literature mp EXACTLY! Impure = lower Ti = higher DT!

Before coming to the next lab… Go to the website: www.ochem.com From the left menu, select

TUTORIALS. From the right column,

PRELECTURES, scroll ¾ of the way down the page.

Watch the following: MASS SPECTROMETRY SPECTROSCOPY (Part 3 of 4) SPECTROSCOPY (Part 4 of 4)

(YOU’LL BE GLAD YOU DID! )

http://www.ochem.com/

CALCULATING DEGREE OF UNSATURATION

CcHhNnOoXx

DU = (2c + 2) – (h – n + x) 2

• 1o unsaturation = 1 C=C or 1 ring• 2o unsaturation = 2 C=C, 2 rings, or CΞC, or combination of C=C &

rings• 3o unsaturation = combination of double bonds, triple bonds, rings• 4o unsaturation = typically indicates an aromatic ring

13C-NMR SPECTROSCOPY d (ppm) = tells what type of carbon

it is.

# signals = tells whether or not there is symmetry within the molecule.

13C NMR CHEMICAL SHIFT CORRELATION CHART

220 210 200 180 160 140 120 100 80 60 40 20 0

R C H

O

R C R

O

190-220d

R C OR

O

R C OH

O

160-190d

R C NR2

O

R C X

O

110-160d

C C 50-110d

C C

Csp3

Fn

0-50d

sp3C Csp3

4o--3o--2o--1o

p. 118 in lab manual

13C NMR Spectral Analysis

70.98 d

46.46

d

29.20 d 17.67

d

14.68 d

C#d

(ppm)C#

d (ppm)

1a 1a 22.341b 1b2 23 34 4 20.915 5

OH

1a

1b

2

3

4

5 1b

1a

2

3

4

5

145.95

d

109.87

d 22.34d

20.91 d

40.16

d 13.79d


1H-NMR SPECTROSCOPY d (ppm) = tells what type of proton it

is.

# signals = tells whether or not there is symmetry within the molecule.

Integration = tells # protons of each type.

Multiplicity = tells # neighboring protons, using

n + 1 rule.

1H-NMR SPECTROSCOPY 12 11 10 9 8 7 6 5 4 3 2 1 0

RC

OH

O

R

CH

O

H

C C

H

H C C H

C H

Fn

sp3C H 10.0-12.0

d9.0-10.0 d

6.5-8.5 d

5.0-6.5 d

2.0-4.5 d

0.0-2.0 d(3o > 2o > 1o)

1H-NMR Spectral Analysis

H#

d (ppm)

Int. Mult. H# d (ppm)

Int. Mult.

1a

1a

1b

1b 4.66 4.70

1 1 s s

2 2.04 1 s 2 X X X3 34 45 5

OH

1a

1b

2

3

4

51b

1a

2

3

4

5

1.20 d6H, s

2.04 d1H, s

1.44 d2H, t

1.38 d2H, hex

0.93 d

3H, t

4.66 d1H, s 1.46 d

2H, pent

1.99 d2H, t

1.71 d3H, s

0.90 d3H, t

4.70 d1H, s

Notice some signals are already assigned for you in the tables!


IR Spectral Analysis

Functional Group

Base Values (cm-1)

2-methyl-2-pentanol

2-methyl-1-

penteneFrequency

(cm-1)Frequency

(cm-1)

OH stretch

3200-3600

X

C-O stretch

1000-1300

X

sp3 CH stretch

2800-3000

sp2 CH stretch

3000-3100

X

C=C stretch

1600-1680

X

29653616 1162

3076

2962

1661

OH

MASS SPECTROMETRY—How it works

Small amount of sample is vaporized into the ionization source, then bombarded with high energy electrons.

When a high energy electron hits the organic molecule, it dislodges a valence electron, to produced a radical cation, called the molecular ion.

M M+ e- + 2 e-Ionization molecular ion

(= radical cation)


Electron bombardment transfers so much energy that the bonds in the cation fragments begin to break.

Some pieces retain the positive charge, some are neutral.

M m1+ + m2

Fragmentation to: cation radical (= neutral loss)


Fragments then flow through a strong magnetic field, where the charged fragments are sorted onto a detector based on their mass to charge ratio (m/z).

Since the charge number on each ion is usually +1, the value of m/z for each ion simply = mass.

The output is a plot of the m/z value of each fragment based on based on its relative abundance.Relative

abundance of

fragment

Mass of fragme

nt

MASS SPECTROMETRY—Interpretation

The way molecular ions break down can produce characteristic fragments that help in identification Serves as a “fingerprint” for comparison

with known materials in analysis (used in forensics)

Positive charge goes to fragments that best can stabilize it

MASS SPECTROMETRY—Interpretation

H C

H

H

H3C C

H

H

H C

C

H

H

C

H

H

C

H

H

H3C C

H

CH3

H3C C

CH3

CH3

Methyl < Primary < Allylic ~ Benzylic ~ Secondary < Tertiary

Increasing carbocation stability

Positive charge goes to fragments that best can stabilize it!

Carbocation stability is discussed in McMurry text, p. 377.

MASS SPECTROMETRY—Alcohols

Functional groups cause common patterns of cleavage in their vicinity

Alcohols undergo -cleavage (at the bond next to the C-OH) as well as loss of H-OH to give C=C

MASS SPECTROMETRY—Alkenes

Important fragment in terminal alkenes is the allyl carbocation at m/z = 41 due to the following cleavage:

R CH2 CH CH2 R CH2 CH CH2 CH2CHH2C

resonance stabilized allyl carbocation

MASS SPECTROMETRY—Carbonyl compounds

A C-H that is three atoms away leads to an internal transfer of a proton to the C=O, called the McLafferty rearrangement

Carbonyl compounds can also undergo cleavage

Mass Spectral Analysis

102

59

84

69

m/z Cation formul

a

Structure m/z Cation formula

Structure

102(M+)

C6H14O

Molecular Ion 84(M+)

C6H12 Molecular Ion

59(base)

C3H7O Cationic Fragment

69(base)

C5H9 Cationic Fragment

OH

Mass Spectral Analysis

m/z Cation formul

a

Structure m/z Cation formula

Structure

102(M+)

C6H14O

Molecular Ion 84(M+)

C6H12 Molecular Ion

59(base)

C3H7O Cationic Fragment

69(base)

C5H9 Cationic Fragment

OH

OH

OH

Final Lab Report In Lab…

Each student will perform all calculations in their own laboratory notebooks and submit yellow copies to instructor for grading.

Post Lab… Each lab group will submit ONE copy of a

typewritten, paragraph style report addressing all points listed for REACTION #2.

All data tables for REACTION #1 and REACTION #2 must be completed and copied into the document.

Original copies of tables provided from the course website are UNACCEPTABLE.

Exp. 13*:

Documents

Transcript of Exp. 13*: