Question

What is the most useful information you can get from a `C^13 NMR` spectrum?

Answer 1

The most useful information you can get from a `""^13"C"` NMR spectrum is the number of non-equivalent carbon atoms.

For example, you have the `""^13"C"` NMR spectrum of an unknown ester.

Is its structure (a) CH₃CH₂COOCH₂CH₂CH₃, (b) CH₃CH₂COOCH(CH₃)₂, or (c) CH₃COOC(CH₃)₃?

You quickly calculate that

(a) has 6 different C atoms;
(b) has two equivalent C atoms, so there only 5 different carbon environments;
(c) has three equivalent C atoms, so there only 4 different carbon environments.

The spectrum shows 5 carbon signals, so the ester must be (c) isopropyl propanoate.