Question

Use equations to show the fragmentation leading to each numbered peak in the mass spectrum of octane-2-one .

Short answer

When high-energy electron hits an organic compound, it removes one of the electrons from the molecule and hence produces positively charged ions known as the molecular ions.

The molecular ion is not only acting as a cation but also as a free radical because of the presence of an odd number of electrons. Hence, it can be called as enol radical cation.

Step-by-step solution

Molecular ion

When high-energy electron hits an organic compound, it removes one of the electrons from the molecule and hence produces positively charged ions known as the molecular ions.

The molecular ion is not only acting as a cation but also as a free radical because of the presence of an odd number of electrons. Hence, it can be called as enol radical cation.

McLafferty rearrangement

The characteristic fragmentation of the molecular ion of a carbonyl compound ( ketones and aldehydes) having at least one gamma hydrogen is known as the McLafferty rearrangement.

Equations for fragmentation of  octane-2-one.