The high-resolution mass spectra of aliphatic aldehydes

The mass spectra of the C₃ to C₉ n-alkanals and a number of branched aldehydes have been obtained at a resolution sufficient to resolve the O? CH₄ doublets. From the resolved spectra, a study of metastable transitions, and the spectrum of one deuterium-labelled alkanal, (n-hexanal-2,2-d₂) the major fragmentation reactions have been elucidated. Of particular interest are the γ-cleavage reaction, leading to [C₃H₅O]+ in the n-alkanals, which proceeds both by a simple cleavage and by cleavage preceded by hydrogen interchange, and the loss of C₂H₄, which involves loss of the C₂ and, probably C₃, carbons.