Spin-spin coupling in proton NMR spectra 92-93

Question 1

What is spin-spin coupling generally?

Answer 1

Some signals in an NMR spectrum may be split into distinctive patters. - This splitting is called spin-spin coupling and arises from interactions with the spin states of protons on adjacent carbon atoms. - The splitting pattern can be used to find the number of protons on an adjacent carbon atom.

Question 2

What do the sub-peaks show?

Answer 2

The number of sub-peaks matches the number of magnetic fields. - The number of sub-peaks in the splitting pattern has nothing to do with the number of protons on that carbon. Spin-spin coupling indicates the number of hydrogen atoms on the adjacent carbon.

Question 3

Explain how the n + 1 rule allows to predict the splitting pattern in NMR spectroscopy.

Use this rule to predict the number of sub-peaks, and the ratio of peak areas within the multiplet for 0,1,2,3 protons on adjacent carbon atoms

Answer 3

• For n protons on an adjacent carbon atom, the number of peaks in a splitting pattern equals n + 1

n n +1 ratio of peak areas within multiplet

0 1 1

1 1+1=2 1:1

2 1+2=3 1:2:1

3 3+1=4 1:3:3:1