Gas phase heats of formation of alkyl immonium ions

Using an energy-resolved electron beam, the gas-phase heats of formation of [CH 2 NH 2 ] + , [CH 3 CHNH 2 ] + , [CH 3 NHCH 2 ] + , [(CH 3 ) 2 CNH 2 ] + , [(CH 3 ) 2 NCH 2 ] + , [CH 3 CHNHCH 3 ] + , [CH 3 CH 2 NHCH 2 ] + , and [CH 3 CH 2 CHNH 2 ] + ions have been measured from their appearance energies in ionic dissociations. All of these ions can have a quaternary immonium structure as one of the canonical forms and are consequently more stable than other isomers. Introduction of the —NH 2 group into a CH 3 + ion brings about a decrease of over 4 eV in the heterolytic bond dissociation energy D(R + —H − ), with slightly larger decreases for —NHR and —NR 2 groups.