PHOTO-IONIZATION OF THE C-1-C-4 MONOSUBSTITUTED ALKYL BENZENES - THERMOCHEMISTRY OF [C7H7]+ AND [C8H9]+ FORMATION

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. Copyright © 1979 John Wiley & Sons, Ltd.