# Why is CDCl_3 a triplet in C^13 NMR?

Jan 9, 2015

The deuterium in the CDCl₃ splits the $\text{^13"C}$ signal into a triplet.

Whenever you run a $\text{^13"C}$ spectrum in CDCl₃, you always get a triplet solvent peak at 77.5 ppm.

For example, here's a spectrum of t-butyl chloride.

You see the characteristic CDCl₃ triplet at 77.5 ppm.

The reason is that $\text{^2"H}$ has a spin quantum number $I$ = 1.

A nucleus with $I = 1$ has $2 I + 1 = 3$ possible orientations.

These orientations have the same energy in the absence of a magnetic field.

In the presence of a magnetic field, these energy levels split. Each level is labelled with a magnetic quantum number $m$ = +1, 0, -1.

So a $\text{^13"C}$ nucleus will be split into three different energy levels depending on the +1, 0, or -1 orientation of the deuterium atom.

Each orientation has the same probability, so the signal is a 1:1:1 triplet.