h nuclear magnetic resonance chemical shifts -...

1H Nuclear Magnetic Resonance

Alkanes

ab

CH3CH2CH2CH2CH2CH2CH2CH3a

octane

a

b

coupling constants

R CH3

R2 CH2

CHR3

1.2-1.7 ppm

1.4-1.7 ppm

0.7-1.3 ppm

chemical shifts

C CHbHa

Jab = 6-8 Hz


Alkanes

2-methylheptane

cCHCH2CH2CH2CH2CH3CH3

CH3a

aa

b

R CH3

R2 CH2

CHR3

1.2-1.7 ppm

1.4-1.7 ppm

0.7-1.3 ppm

chemical shifts

a

c

b

e c

d

b

a


Alkenes

2-methyl-1-pentene

d

eCH3CH2CH2

CC

CH3

H

Ha b c

coupling constants

C C-H

1.6-2.6 ppm

4.5-6.5 ppm

chemical shifts

C C-C-H

C CHbHa

C CHa

HbC C

Ha

HbC C

Ha

CHc

Jab = 0-3 Hz Jab = 0-3 HzJab = 6-14 Hz Jab = 11-18 Hzcis trans geminal allylic


Aromatic Compounds

4-methylbenzyl chloride

b c

d

a

Ar-H

2.3-2.7 ppm

6.5-8.0 ppm

chemical shifts

Ar-C-H

coupling constants

CH3

Cla

bdc

HaHa Ha

HbHbHb

Jab = 0-1 HzJab = 7-10 Hz Jab = 2-3 Hzortho meta para


Alkynes

1-pentyne

d c b

a

coupling constants

1.6-2.6 ppm

1.7-2.7 ppm

chemical shifts

C≡C-H

C≡C-C-H

HCH3CH2CH2

a b dc

HbCHa

Jab = 2-3 Hz


Alkynes

d c

1-pentyne HCH3CH2CH2

a b dc

Δ 2.6 Δ 3.0

Δ 2.5

Δ 2.6

Δ 2.9

Jab = 2.8 Hz Jab = 2.7 Hz


Alkyl Halides

1-chlorobutane

d

c b

a

coupling constants

CH3CH2CH2CH2Cla b dc

CH I

2.7-4.1 ppm

3.1-4.1 ppm

2.0-4.0 ppm

chemical shifts

CH Br

CH Cl

4.2-4.8 ppmCH F

C CFHa

C FHa

JaF = 50 Hz JaF = 20 Hzgeminal vicinal


Alcohols

2-methyl-1-propanol

c

d b

a

coupling constants

4.0-7.0 ppm

3.2-3.8 ppm

chemical shifts

Ar-O-H

R-CH OH

0.5-5.0 ppmR-O-H

cCHCH2-OHCH3

CH3a

ad

b

C OHbHa

Jab = 0-5 Hz


Alcohols

proton exchange

C O-HH

+ C O-HH

+H A H A

D O D H O DC O-HH

+ C O-DH

+

useful for identification

OH proton is exchangeable


Alcohols

proton exchange:

OH

OH


Alcohols

proton exchange

O

HO OO

HO

OH HO OH

HOOH

OH

OH


Ethers

butyl methyl ether

b

e

c d

a

2.5-3.5 ppm

3.2-3.8 ppm

chemical shifts

RO-C-H

O C-H

CH3CH2CH2CH2OCH3a b dc e


Amines

propylamine

c

d

b

a

3.0-5.0 ppm

2.2-2.9 ppm

chemical shifts

Ar-N-H

R-CH NH

0.5-4.0 ppmR-N-H

CH3CH2CH2NH2

a b dc


Aldehydes

2-methylpropanal

c b

a

coupling constants

2.1-2.4 ppm

9.0-10.0 ppm

chemical shifts

C COH

R H

C COH

R H

C COHa

Hb

Jab = 1-3 Hz

a CH3CHCO

HCH3

bc


Aldehydes

2-methylpropanal

c b a

a CH3CHCO

HCH3

bc


Ketones

5-methyl-2-hexanone

a

b

c

2.1-2.4 ppm

chemical shifts

C COH

R R'

d

e e

a b

c dCH3 C

OCH2CH2CHCH3

CH3


Esters

isobutyl acetate

c b

d

2.1-2.5 ppm

3.5-4.8 ppm

chemical shifts

R CO

O

C COH

R OR'

CH

a

a b

c dCH3 C

OOCH2CHCH3

CH3


Carboxylic Acids

ethylmalonic acid

d

c

b

a

2.1-2.5 ppm

10.0-12.0 ppm

chemical shifts

R CO

O

C COH

R OH

H

CH3CH2CHCOOH

a b c d

CO2H


Carboxylic Acids

exchange

OH proton is exchangeable

R OD

O

R OH

OD O D+ H O D+


Amides

butanamide

d

c

b

a

2.1-2.5 ppm

2.2-2.9 ppm

chemical shifts

R CO

N

C COH

R N

CH

5.0-9.0 ppmR CO

N HCH3CH2CH2 C

ONH2

a b c d


Amides

restricted rotation

R N

O

R N

O

R N

OR2

R1R1R2

R1 R2slow


Nitriles

pentanenitrile

d

c

a

2.1-3.0 ppm

chemical shifts

C CH

R N

b

CH3CH2CH2CH2C≡Na b dc


1. Get an Overview • identify any reference solvents and known impurities (e.g. water ca. 1.5 ppm) 2. Integration: • count the number of protons (remember: integration gives you a ratio) • verify proton count based on the molecular formula • determine how many protons are associated with each peak • remember: integration gives you a ratio 3. Chemical Shift: • determine the chemical shift of each resonance in the spectrum

- what functional groups may be present - consider the presence of heteroatoms 4. Multiplicity (Splitting Pattern): • determine how many Hs are near each signal? • determine coupling constants who's coupled to who? - consider the magnitude of the coupling constants as well 5. Put it all Together: • often helpful to put small fragments together and build from there

How to Interpret an NMR Spectrum


Reporting 1H NMR Data

CH3CH2Br

1H NMR (300 MHz, CDCl3) δ 3.43 (2H, q, J = 7.2 Hz), 1.68, (3H, t, J = 7.2 Hz)

318.56 318.06311.23 304.00 303.50 296.56 157.19150.00 142.56

3.5573.552 3.472 3.395 3.389 3.312 1.756 1.675 1.592

11995

396325444156446

1000363

Hzppm Int




318.56 318.06311.23 304.00 303.50 296.56 157.19150.00 142.56

3.5573.552 3.472 3.395 3.389 3.312 1.756 1.675 1.592

11995

396325444156446

1000363

Hzppm Int

7.197.44

7.3

avg3.43

7.33

7.23

7.44

7.3

chemical shift coupling constants

1.68

avg

avg

bromoethane




spectrometer frequency

solvent

chemical shift (to 2 decimal places)

integral value multiplicity

coupling contant(s) – largest first, list to 1 decimal place

singlet (s) doublet (d) triplet (t) quartet (q) pentet (p) sextet septet multiplet (m) etc.

will revisit

h nuclear magnetic resonance chemical shifts -...

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