25

6.2.

Salient Features of an 1H-NMR Spectrum

•Chemical shift
δ= (υobs-υref)/υrefx 106
position in spectrum is determined by the chemical environment
alkyl group

•

•Integration
peak intensities depend on the number of contributing nuclei
•Coupling
•peaks have a fine structure related to the presence of neighbouring nuclei

H

H

H

H

H

H

2J coupling (geminal)

3J coupling (vicinal)

4J coupling (allylic coupling)

J approx. 12Hz

J depends on dihedral angle
approx. 7 Hz in alkyl groups

J typically 1-2Hz

J = Coupling constant (measured in Hz)
through bond coupling - scalar coupling

Rules for coupling

(i)

A nuclei which “sees” (interaction between magnetic fields) n equivalent spin
1/2 nuclei will appear as a series of n+1 lines where the separation of those
lines is determined by the coupling constant J and the relative intensity of the
lines are determined by Pascal’s triangle:

0

1

2

3

4

5

6

7

8

9

10

X-CHR2

alkenes

aromatics

aldehydes

carboxylic acids

ð / ppm

0

1

2

3

4

5

6

7

8

9

10

O

O

H
H

H

H

H

H

H

H

H

H

ð / ppm