C-13 NMR Spectroscopy

CHM 320

La Salle University

C-13 Spectrum of
m-Nitroacetophenone

NO

2

CCH

3

O

1H NMR Spectrum of
Ethylbenzene

CH

2

CH

3

Typical ppm ()Ranges in

C-13 NMR

Relaxation Times

Coupling Constants are

Large

J Values measured in Hz

HC

CCH

2

CH

2

CH

2

CH

3

HC

CCH

2

CH

2

CH

2

CH

3

CH

3

CH

2

OCCH

2

CCH

3

O

O

CH

3

CH

2

OCCH

2

CCH

3

O

O

H

2

C=C=CHCH

2

CH

2

OH

CO

2

H

N

H

3

C

H

3

C

CCH

3

O

Silverstein, p. 212

Silverstein, p. 215

N

H

3

C

H

3

C

CH

OCH

3

OCH

3

C

C

H

NHCCH

3

O

H

3

C

HC

O

CF

3

COCH

3

O

Predicting Chemical

Shifts

Predicted Chemical Shifts

of

C

a

and

C

b

a

b

C

a

= (-2.5) + 4(9.1) + 9.4 + 2(-2.5) + 3(-1.5) + (-8.4) =

25.4 ppm

C

b

= (-2.5) + 2(9.1) + 5(9.4) +(-7.2) + (-2.5) =

53.0 ppm

base



4

o

(1

o

) 4

o

(2

o

)

base



2

o

(4

o

) 2

o

(3

o

)



2,2,4-Trimethylpentane

53.28, 31.10, 30.16, 25.51,

24.73

Chemical Shift

Prediction with
Functional Groups

Use Base Value From

Table 4.5

OH

OH

OH

Using Table 4.5 and 4.6

34.7 + 41 = 75.7

22.8 + 41 = 63.8

13.9 + 48 = 51.9 ppm

You can Choose Which

Base Value from Table

4.5 to Use

OH

OH

34.7 + 41 + (-5) + 3(9.4) + (-2.5) + (-7.2) =

89.2 ppm

C-3 -OH -OH 

2

o

(3

o

) 2

o

(4

o

)

OH

OH

36.9 + 41 + (-5) + 2(9.4) + (-2.5) =

88.8 ppm

C-3 -OH -OH 

2

o

(3

o

)

Spectrum at 75 MHz and

150 MHz