Chapter G, Problem G.2P

Interpretation Introduction

Interpretation:

The base peak in the mass spectrum of an alkane, ${\text{C}}_{\text{7}}{\text{H}}_{\text{16}}$, appears at m/z =$\text{57}$. A molecule that is consistent with this data is to be drawn.

Concept introduction:

The base peak is the tallest peak and corresponds to the most stable ion among the molecular and fragment ions. The peak at m/z = $\text{57}$ corresponds to the formula of ${\text{C}}_{\text{4}}{\text{H}}_{\text{9}}$, which is a tert-butyl cation ${\left({\text{CH}}_{\text{3}}\right)}_{\text{3}}{\text{C}}^{\text{+}}$. If the molecule has a formula of ${\text{C}}_{\text{7}}{\text{H}}_{\text{16}}$, the remaining atoms in the formula are ${\text{C}}_{\text{3}}{\text{H}}_{\text{7}}$, which could be an isopropyl fragment or a propyl fragment. In case of an isopropyl fragment, the molecule is $\text{2, 2, 3-trimethylbutane}$ and in case of propyl fragment, the molecule is $\text{2, 2- dimethylpentane}$.