Chapter G, Problem G.7YT

Interpretation Introduction

Interpretation:

The fragmentation pathway that gives rise to the peak at $\text{m/z = 85}$ in the mass spectrum of $\text{hexan-2-one}$ is to be determined.

Concept introduction:

In mass spectrometry, one of the most important features of a heteroatom is its lone pair of electrons. As nonbonding electrons, lone pairs are typically the least tightly bound electrons in the molecule. In the ionization of a molecule containing a heteroatom, a lone-pair electron is generally the most likely electron lost to produce the molecular ion, ${\text{M}}_{\text{•}}{}^{\text{+}}\text{.}$ Another common fragmentation pathway is elimination of an alkyl group from the carbon atom bonded to the heteroatom – a process known as 𝛂-cleavage.

These two fragmentation pathways – heterolysis and α-cleavage – are also common to other compound classes that have functional groups with heteroatoms, such as amines, ethers, and alcohols. Depending on the identity of the functional group as well as the specific structure of the compound, one of these fragmentation pathways can be highly favored over the other.