Trends in the reactions of gaseous phenyl pnictogen radical cations C6H5EH2 center dot+ (E=N, P, As) Letzel, Matthias Letzel Matthias Grützmacher, Hans-Friedrich Grützmacher Hans-Friedrich Stein, Daniel Stein Daniel Grützmacher, Hansjörg Grützmacher Hansjörg pnictogens C6H5EH2, E = N ( 1), P ( 2), and As ( 3), the mass spectrometric reactions of phenyl phosphane 2 have been re-investigated by D-labeling and by using methods of tandem mass spectrometry. The 70 eV mass spectrum of 2 shows the base peak for ion [ M- 2H](center dot+) and significant peaks for ions [ M-H](+), [ M-( 2C, 3H)](+), [ M- PH](center dot+), and [ M-( C, P, 2H)](+). Metastable 2(center dot+) fragments exclusively by loss of H-2, and the investigation of deuterated 2-d(2) shows that excessive H/D migrations occur before fragmentation. Other significant fragment ions in the mass spectrum of 2 arise by losses of C2H2, P, or HCP from the ion [M-H](+). This mass spectrometric behavior puts the radical cation 2(center dot+) in between the fragmentation reactions of aniline radical cation 1(center dot+) ( loss of H and subsequent losses of C2H2, or HCN) and phenyl arsane radical cation 3(center dot+) ( elimination of H2 and loss of As from ion [ M- H]+). The fragmentation mechanisms of the radical cations 1(center dot+)-3(center dot+) and of related ions were analyzed by calculations of the enthalpy of relevant species at the stationary points of the minimum enthalpy reaction pathways using the DFT hybrid functionals UBHLYP/6-311+G(2d,p)// UBHLYP/ 6- 311+ G( d). The results show that, in contrast to ionized aniline 1(center dot+), the reactions of the derivatives 2(center dot+) and 3(center dot+) of the heavier main group elements P and As are characterized by an easy elimination of H2 via a reductive elimination of group C6H5- E ( E = P, As) and by a special stability of bicyclic isomers of 2(center dot+) and 3(center dot+). Thus, while 1(center dot+) rearranges by ring expansion and formation an 7-aza-tropylium cation by loss of H center dot, the increased stability of bicyclic intermediates in the rearrangement of 2 center dot+ and in particular of 3(center dot+) results in separate rearrangement pathways. The origin of these effects is the more extended and diffuse nature of the 3p and 4p AO of P and As. 25 3282-3291 3282-3291 ROYAL SOC CHEMISTRY 2008 1