Analysis of Alcohols : In alcohols the molecular ion may be altogether absent. The predominant fragmentation involves loss of an alkyl group. In case of branched alcohols, the largest alkyl group is usually lost.

In the spectrum of 1-butanol, the base peak is obtained at m/z =31 due to loss of a propyl group. Butan-2-ol loses an ethyl group to have base peak at m/z = 45. Similarly, 2-methylpropan-2-ol loses a methyl group to give a peak corresponding to m/z = 59.

A second common mode of fragmentation is dehydration. Alcohols having four or more carbons may undergo simultaneous loss of ethylene and water.