Question

An unknown with a boiling point of 178 C and an index of refraction of 1.4113 and classified as an ester was considered to be n-heptyl formate, n-hexyl acetate, or isoamyl n-butyrate (isopentyl n-butyrate). If the proton NMR spectrum of the unknown was available, how might it be used to identify the unknown? If the IR spectrum of the unknown was available, how might it be used to identify the unknown?

Answer 1

Among three (n-heptyl formate, n-hexyl acetate, or isoamyl n-butyrate), we can easily identify n-heptyl formate from protan NMR and IR spectrum because it has aldehyde group (CHO).

Aldehyde proton comes around 8.04 ppm range in proton NMR and in IR spectrum we can identify aldehyde C-H two weak bands around 2700-2900 cm^-1 range.

isoamyl n-butyrate and n-hexyl acetate we can identify by using NMR easily but by using IR it is difficult.

For isoamyl n-butyrate, we can observe doublet at around 0.91 ppm range for two methyl groups which cannot be observed in the case of n-hexyl acetate.

In n-hexyl acetate case, we can observe one singlet at 2.20 ppm range for methyl group.