Question

Question: What cations are formed in the mass spectrometer by α cleavage of each of the following compounds?

Short answer

Answer

Step-by-step solution

Fragmentation of organic compounds

When an organic compound in the gaseous phase is bombarded with electrons, the ionization electron of the compound is removed.

This causes the formation of a molecular ion with high energy. The molecular ion stabilizes by fragmentation into shorter fragments.

Alpha-cleavage

A common mode of fragmentation in molecular ions with a functional group is alpha-cleavage in which $\mathrm{C}-\mathrm{C}$bond is broken at the alpha position of the functional group.

An alpha-cleavage of molecular ion produces a cation and a free radical.

The cation travels through a mass spectrometer and produces a line in the mass spectrum while free radical is removed by the vacuum pump.

Alpha-cleavage of given compounds

(a) Alpha-cleavage can be done on either side of the carbonyl group forming 2 products.

Alpha-cleavage of (a)

(b) Alpha cleavage occurs at the alpha position of the hydroxyl group

alpha-cleavage of (b)

(c) Alpha-cleavage can occur at either side of the carbonyl group

Alpha-cleavage of (c)