Regioselective hydride abstraction and proton transfer in gaseous ion/molecule complexes: methyl substituent effects on the fragmentation of protonated 1-(4-tert-butylphenyl)-3-phenylpropanes

Eur. J. Mass Spectrom. 1, 445–455 (1995)
DOI: 10.1255/ejms.104

Regioselective hydride abstraction and proton transfer in gaseous ion/molecule complexes: methyl substituent effects on the fragmentation of protonated 1-(4-tert-butylphenyl)-3-phenylpropanes

Carsten Matthias, Katrin Weniger and Dietmar Kuck^*
Fakultät für Chemie, Universität Bielefeld, Universitäts straße25, D-33615 Bielefeld, Germany.

ABSTRACT:

Gas-phase protonolysis of 1-(4-tert-butylphenyl)-3- phenylpropanes bearing a methyl substituent at one of the arene rings gives rise to competing losses of isobutane and isobutene via intermediate, purely hydrocarbon, ion/molecule complexes [Me₃C⁺C₆H₅CH₂CH₂CH₂–C₆H₄CH₃]. The hydride transfer within the complexes occurs preferentially from the CH₂ group of the methylated benzyl unit (in the order p-CH₃ >m-CH₃ > o-CH₃ ~ H) and irrespective of the ring from which the tert-butyl group has been released originally. The reciprocal proton transfer gains importance with increasing proton affinity of the substituted benzene nucleus (p-CH₃< o-CH₃ < m-CH₃), again independent of the original substitution pattern. Thus, the reactivity of thetert-butyl cation within the complex (as a Lewis and a Brønsted acid) is governed by the whole of the electrostatically bound 1,3-diarylpropane neutral.

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