Chapter G, Problem G.4P

Interpretation Introduction

Interpretation:

The mass spectrum of an alkene, ${\text{C}}_{\text{8}}{\text{H}}_{\text{16}}$, exhibits a peak at m/z = $\text{41}$. Two isomers that are consistent with this data are 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 Index of Hydrogen Deficiency (IHD) for ${\text{C}}_{\text{8}}{\text{H}}_{\text{16}}$ is $\text{1}$, and the molecule has $\text{C=C}$ bond. The mass peak at m/z = $\text{41}$ corresponds to propenyl cation, which is ${\text{CH}}_{\text{2}}{\text{=CH-CH}}_{\text{2}}{}^{\text{+}}$. Many possible isomers with the formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{16}}$ would give this fragment. The essential part is that the $\text{C=C}$ bond must be terminal to produce the fragment ion ${\text{CH}}_{\text{2}}{\text{=CH-CH}}_{\text{2}}{}^{\text{+}}$.