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

Gas-phase protonolysis of 1-(4-tert-butylphenyl)-3-phenylpropanes bear ing a methyl substituent at one of the arene rings gives rise to compe ting losses of isobutane and isobutene via intermediate, purely hydroc arbon, ion/molecule complexes [Me(3)C(+) C6H5-CH2CH2CH2-C6H4CH3]. The hydride transfer within the complexes occurs preferentially from the C H2 group of the methylated benzyl unit (in the order p-CH3 > m-CH3 > o -CH3 approximate to H) and irrespective of the ring from which the ter t-butyl group has been released originally. The reciprocal proton tran sfer gains importance with increasing proton affinity of the substitut ed benzene nucleus (p-CH3 < o-CH3 < m-CH3), again independent of the o riginal substitution pattern. Thus, the reactivity of the tert-butyl c ation within the complex (as a Lewis and a Bronsted acid) is governed by the whole of the electrostatically bound 1,3-diarylpropane neutral.