1

Carbon-13 12C is not NMR-active (no magnetic spin (I = 0))

13C has a magnetic spin (I = 1/2 , odd mass) 13C signals are 6000 times weaker than 1H because:

1. Natural abundance of 13C is small (1.08% )

2. Magnetic moment of 13C is small The gyromagnetic constant of 13C is one-fourth of that of 1H The chemical shift range is larger than for protons

0 - 200 ppm The number of different signals indicates the number of

different kinds of carbon PULSED FT-NMR is required

13C g = 6.72 1H g = 26.75

2

3

Coupling Constants

However, 13C does couple to hydrogen atoms (I = 1/2)

13C - 13C coupling NO! not probable

very common13C – 1H coupling YES!

4

Coupling to attached Protons

5

Decoupling the Proton Spins

Off-resonance decoupling

Proton-Decoupled Spectra

6

Ethylphenylacetate

7

Some Instruments Show The Multiplicities of The Peaks on The Decoupled Spectra

s = singlet t = tripletd = doublet q = quartetCODE :

8

Hydrogen and Carbon Chemical Shifts

9

Correlation chart for 13C Chemical Shifts (ppm)

10

Approximate Chemical Shift Ranges (ppm) for Selected Types of Carbon.

11

1-Propanol

12

2,2-Dimethylbutane

13

Bromocyclohexane

14

Cyclohexanol

15

Cyclohexene

16

Cyclohexanone

17

Toluene

18

Cl

Cla

a

b

b

c

c

1,2-Dichlorobenzene

19

1,3-Dichlorobenzene

20

Estimation of Carbon Chemical shifts in Substituted Benzene