Fragmentation pattern and mass spectra of Alcohols

·        Molecular ion peak of primary and secondary alcohol is quite small and for tertiary alcohol is undetectable.

·        Molecular ion peak is formed by the removal of one electron from the lone pairs on the oxygen atom of primary and secondary alcohol.

·        Cleavage of C-C bond next to the oxygen (α cleavage) is of general occurrence.

o   Thus primary alcohol  show a prominent peak resulting from oxoniumion (m/z 31)

o   secondary alcohol show a prominent peak resulting from (m/z 45,59,73 etc)

o   tertiary alcohol show a prominent peak resulting from(m/z 59, 73, 87 etc)

·     A distinct and sometimes prominent peak can usually be found at M-18 from loss of H₂O.

·     In primary alcohol elimination of water, together with elimination of alkene, accounts for the presence of a peak at M-(alkene+ H₂O) ie (m/z 46, 74, 102 etc)

lets examine spectrum of 1-pentanol

examine spectrum of  secondary alc. 2-pentanol

now examine spectrum of  tertiary alc. 2-methyl-2-butanol

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