Chapter G, Problem G.6YT

Interpretation Introduction

(a)

Interpretation:

The $\text{α-}$ cleavage pathway of $\text{diisopropyl ether’s}$ molecular ion that accounts for the mass peak at $\text{m/z = 87 }$ 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.

Interpretation Introduction

(b)

Interpretation:

The $\text{α-}$ cleavage pathway of $\text{pentan-1-ol’s }$ molecular ion that accounts for the mass peak at $\text{m/z = 31}$ 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.