Question

Explain how the following compounds, each with the same molecular formula, could be distinguished by their 1 H NMR spectra.

Short answer

• The protons NMR spectrum of compound A gives three signals, and the splitting of these signals are triplet, triplet, and multiplet.
• The proton NMR spectrum of compound B also gives three signals, and the splitting of these signals are doublet, multiplet, and doublet.
• The proton NMR spectrum of compound C also gives two signals, and splits these signals in triplet and quadrat.

Step-by-step solution

Equivalent protons

The protons connected to the same kind of atoms are equivalent.

• There are three sets of equivalent protons in the first compound (A) as 2,2,1.
• There are three sets of equivalent protons in the second compound (B) as 2,1,1.
• There are two sets of equivalent protons in the third compound (C) as 3 and 2.

Spin-spin splitting

A signal splitting can occur by the N+1 rule, where N is the neighboring protons.

• In the first compound, one signal is 2+1 is triplet, one 2+1 and 1+1 is a multiplet, and the third is 2+1 is a triplet.
• In the second compound, one signal is 1+1 is a doublet, one 2+1 and 1+1 is a multiplet, and the third is 1+1 is a doublet.
• In the third compound, one signal is 2+1 is a triplet, and the other 3+1 is the quadrate.

C is easiest to distinguish from the other two’s, as it is having only two signals.

A and B can be distinguished by splitting of signals.