Chapter G, Problem G.7P

Interpretation Introduction

Interpretation:

The mass spectrum of an alcohol (${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$) exhibits a base peak at m/z = $\text{59}$. Whether the alcohol is most likely $\text{pentan-1-ol}$, $\text{pentan-2-ol}$, or $\text{pentan-3-ol}$ is to be explained.

Concept introduction:

The mass of each ${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$ compound is $\text{ 88}$ u.

The molecular ion is produced from the loss of a nonbonding electron on $\text{O}$. The peak at m/z = $\text{59}$ is due to loss of $\text{29}$ u from the molecular ion, which is an ethyl radical, $\text{CH}\text{C}{\text{H}}_{\text{2}}{}^{\text{•}}$. This leaves the cation ${}^{\text{+}}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{CH-OH}$ at m/z = $\text{59}$. Therefore, the peak at m/z = $\text{59}$ corresponds to the loss of an ethyl radical from ${\text{M}}^{\text{+}}$ via $\text{α-}$ cleavage. This can come only from the fragmentation for $\text{pentan-3-ol}$.