Question

The proton and ¹³C NMR spectra of a compound of formula C₄H₁₁N are shown here. Determine the structure of this amine, and give peak assignments for all of the protons in the structure.

Short answer

The structure of the amine deduced is butan-2-amine.

Peaks and respective chemical shifts have been assigned for the protons in the structure,

Step-by-step solution

Structure deduction from given spectrum:

A compound with formula C₄H₁₁Nhas no elements of unsaturation. The proton NMR shows five types of hydrogen with the amino group appearing as a broad peak at chemical shift value 1.15, meaning that there are four different groups of hydrogens on the four carbons. The carbon NMR also shows four carbons, so there is no symmetry in this structure, means it does not contain a tert-butyl group or an isopropyl group.

Structure deduction from chemical shifts and splitting pattern:

In the given proton NMR spectrum, the multiplet farthest downfield is a methine carbon deshielded by nitrogen and integration shows it to be one hydrogen. There is a 2H multiplet at chemical shift value 1.35, the broad peak of amino group at chemical shift value 1.15 and a 3H doublet at chemical shift value 1.05 and a 3H triplet at chemical shift value 0.90. The latter two signals must represent methyl groups next to a methine carbon and a methylene carbon respectively.

So far, we have the following fragments:

The fragments shown above have one carbon too many, so there must be one carbon that is duplicated, thus the only possible one is methine carbon and the structure reveals itself: