The mass spectra of isomeric hydrocarbons—II: The C5H8S isomers, spiropentane, cyclopentene, 1,3‐pentadiene and isoprene; The mechanisms and energetics of their fragmentations

The mass spectra of spiropentane, cyclopentene, 1,3‐pentadiene (piperylene), isoprene and some deuterium labelled analogues have been studied. The heats of formation of the molecular ions and the major daughter ions [C5H7]+ and [C4H5]+ have been estimated. Fragmentation of these molecules mostly proceeds via common intermediates in which hydrogen atoms have lost their positional identity. Only spiropentane displays any specific fragmentation behaviour related to its ground state geometry.