Organic Chemistry

Section 14.7 Characteristic Values of Chemical Shifts 537

In a similar environment, the signal

for methyl protons occurs at a lower

frequency than the signal for methylene

protons, which in turn occurs at a lower

frequency than the signal for a methine

proton.

for the bprotons is at a lower frequency because methyl protons appear at a lower
frequency than do methylene protons in a similar environment.

The signal for the aprotons of 2-methoxypropane is the signal at the lowest
frequency in the NMR spectrum of this compound because these protons are far-
thest from the electron-withdrawing oxygen. The band cprotons are the same dis-
tance from the oxygen, but the signal for the bprotons appears at a lower frequency
because, in a similar environment, methyl protons appear at a lower frequency than
does a methine proton.

1 H

butanone

2-methoxypropane

bca

a

ac b

CH 3 CH 2 CCH 3

O

CH 3 OCHCH 3

CH 3

Tutorial:

NMR chemical shifts

Table 14.1

Approximate

chemical shift

(ppm)

Approximate

chemical shift

Type of proton Type of proton (ppm)

Approximate Values of Chemical Shifts for^1 H NMRa

(CH 3 ) 4 Si 0

CH 3 0.9

CH 2

CH

CCCH 3

1.3

1.4

1.7

C

O

O

CH 3

CH 3

2.1

C

O

OH

C

O

NH 2

Variable, 10– 12

Variable, 5– 8

CCH 2.4

ROCH 3 3.3

R

R

CCH 2

RNH 2

4.7

R

RR

CHC 5.3

2.3

H 6.5– 8

C H 9.0– 10

I C H 2.5– 4

Br C H 2.5– 4

Cl C H 3 – 4

F C H 4 – 4.5

Variable, 1.5– 4

ROH Variable, 2– 5

ArOH Variable, 4– 7

aThe values are approximate because they are affected by neighboring substituents.