Gaseous [C^sub n^H^sub 2n+1^^sup +^ ... 1,3-Diphenylpropane] Ion/Neutral Complexes Containing Alkyl Cations of Different Acidities and Hydride Ion Affinities

Gaseous ion/neutral (I/N) complexes [R^sup +^ ... C^sub 6^H^sub 5^CH^sub 2^CH^sub 2^CH^sub 2^C^sub 6^H^sub 5^] with R = t-C^sub 4^H^sub 9^^sup +^, s-C^sub 4^H^sub 9^^sup +^ and s-C^sub 3^H^sub 7^ ^sup +^ have been generated by protonation of the corresponding precursor compounds, R-C^sub 6^H^sub 2^CH^sub 2^CH^sub 2^CH^sub 2^C^sub 6^H^sub 5^, in the chemical ionisation (CI) source of a sector-field mass spectrometer. The fragmentation of these I/N complexes and several deuterium-labelled isotopologues on the metastable ions' timescale (20.30 µs), as studied by MIKE spectrometry, revealed that (i) the initial ring position (meta- or para-) of R = t-C^sub 4^H^sub 9^^sup +^ does not affect their intra-complex reactivity, (ii) the fragmentation of the s-C^sub 3^H^sub 7^ ^sup +^ and s-C^sub 4^H^sub 9^^sup +^ ions is dominated by proton transfer to the 1,3-diphenylpropane neutral but hydride ion abstraction in the reverse direction competes to a minor extent, (iii) the secondary alkyl cations exhibit the same regioselectivity (k^sub α-H^/k^sub ω-H^ = 1.0) and kinetic isotope effect (k^sub H^/k^sub D^ = 1.6) in the hydride transfer channel as do tertiary alkyl cations, (iv) the s-C^sub 4^H^sub 9^^sup +^ ions do not undergo skeletal isomerisation to t-C^sub 4^H^sub 9^^sup +^ ions within the I/N complex. Attempts to characterise the trimethylsilyl complex, [Si(CH^sub 3^)^sub 3^^sup +^ ... C^sub 6^H^sub 5^CH^sub 2^CH^sub 2^CH^sub 2^C^sub 6^H^sub 5^], by CI/MIKE spectrometry under analogous conditions failed. [PUBLICATION ABSTRACT]