Chapter 25: Q41P (page 1030)

Question. The mass spectrum of tert-butylamine follows shows an intense base peak at m/z58, and very little else. Use a diagram to show the cleavage that accounts for the base peak. Suggest why no molecular ion is visible in this spectrum.

Short Answer

Expert verified

This fragmentation is favorable because the iminium ion produced is stabilized by resonance.Also, there are three possible cleavages that give the same ion. Both these factors combine to make the cleavage facile, at the expense of the molecular ion, hence no molecular ion is visible in the spectrum.

Step by step solution

Step-1. Molecular ion peak, base peak:

Base peak is the most intense or tallest peak in a mass spectrum due to the ion with the greatest relative abundance.Base peaks are not molecular ions. The peak representing the molecular ion is called the molecular ion peak. Excluding any peaks due to the presence of heavier isotopes, the molecular ion peak is the peak with highest mass to charge ratio.

Step-2. Cleavage in tertiary butylamine and reason for why no molecular ion occurs:

This fragmentation is favorable because the iminium ion produced is stabilized by resonance. Also, there are three possible cleavages that give the same ion. Both these factors combine to make the cleavage facile, at the expense of the molecular ion, hence no molecular ion is visible in the spectrum.

Cleavage pattern in tertiary butylamine