Chapter G, Problem G.8P

Interpretation Introduction

Interpretation:

The mass spectrum of a ketone (${\text{C}}_{\text{7}}{\text{H}}_{\text{14}}\text{O}$) exhibits a base peak at m/z = $\text{57}$. Whether the ketone is most likely $\text{heptan-2-one}$, $\text{heptan-3-one}$, or $\text{heptan-4-one}$ is to be explained.

Concept introduction:

The mass of each compound is $\text{114}$ u.

In each case, the molecular ion is produced from the loss of a nonbonding electron on $\text{O}$. The peak at m/z = $\text{57}$ is due to loss of a butyl radical, ($\text{57}$ u), to produce the acylium cation, ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{C}\equiv {\text{O}}^{\text{+}}$. $\text{Heptan-3-one}$ is the only compound capable of losing a butyl radical from $\text{α}$ -cleavage.