Fragmentation Patterns of Alcohols, Phenols, and Thiols

The intensity of the molecular ion peak in the mass spectrum of a primary or secondary alcohol is usually rather low, and the molecular ion peak is often entirely absent in the mass spectrum of a tertiary alcohol. Common fragmentations of alcohols are a-cleavage adjacent to the hydroxyl group and dehydration. 

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2- Pentanol (Fig. 4.28) loses either a propyl group to form the CH3CH=OH fragment at mk = 45 or a methyl radical to form the relatively small peak at mIz = 73 corresponding to CH3CH2CH2CH=OH.  

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