Photoionization of the C‐1-C‐4 monosubstituted alkyl benzenes: Thermochemistry of [C7H7]+ and [C8H9]+ formation

Abstract
The appearance energies for the [C7H7]+ and [C8H9]+ fragment ions produced in the fragmentation of the C‐1C‐4 monosubstituted alkyl benzenes have been measured by photon impact. The mean heat of formation calculated for [C7H7]+ is 205.3 ± 1.9 kcal mol−1 which is consistent with a threshold tropylium structure. For [C8H9]+ the mean heat of formation is calculated to be 199.2 ± 1.3 kcal mol−1 which can be equated with either a methyl tropylium or α‐phenylethyl structure at threshold. Some evidence is provided for the existence of the α‐phenylethyl ion.