Reactivity of Mixed and Neat Proton Bound Dimers of Acetonitrile and Methyl Acetate

Reactions of the proton bound mixed dimer (CH 3 CN)(CH 3 COOCH 3 )H + with a series of base molecules are compared with the analogous reactions of the corresponding neat dimers (CH 3 CN) 2 H + and (CH 3 COOCH 3 ) 2 H + . Reactions observed are ligand association, ligand switching and proton transfer to the base. The association−insertion reaction of ammonia, methylamine, and dimethylamine reported earlier is much more prevalent in the case of the neat dimers than in the mixed one. Oxygen containing base molecules, CH 3 CHO, CH 3 OCH 3, CH 3 COCH 3, CH 3 COOC 2 H 5, and CH 3 OCH 2 CH 2 OCH 3 switch out preferentially the acetonitrile from the mixed dimer while nitrogen-containing bases, NH 3, CH 3 NH 2, Me 2 NH, Me 3 N, and Et 3 N switch out preferentially the methyl acetate. This result is rationalized on the basis of the energetics of the corresponding reactions which are deduced from correlations with proton affinities and gas-phase basicities.