The mass spectrometric fragmentation of n‐heptane

The electron impact fragmentation of n ‐heptane has been investigated using 13 C labelled derivatives. A mechanism is proposed for the loss of alkyl radicals where the cleavage of a CC bond is coupled with the rearrangement of a hydrogen atom, thus yielding a secondary alkyl ion that eventually fragments further by a subsequent loss of olefin. For alkyl ions with less than six carbon atoms this consecutive pathway is in competition with formation directly from the molecular ion. The consecutive pathway contributes about 15% to the intensity of the alkyl ions with four and five carbon atoms and 80% for smaller ions. The electron energy dependence was studied.