Binding interaction of the trimethylgermyl cation with acetophenones in the gas phase

Abstract

The gas-phase basicities towards the trimethylgermyl cation, GB(Me₃Ge⁺), were determined for a series of acetophenones by measuring the equilibrium constants of trimethylgermyl cation transfer reactions. The effects of ring substituents on the Me₃Ge⁺ basicities are excellently correlated in terms of the Yukawa–Tsuno equation, giving a ρ value of −7.1 and an r⁺ value of 0.71. These results suggest that the binding interaction of Me₃Ge⁺ with the O atom of the carbonyl group of the acetophenones has a pronounced covalent character, resulting in the development of a positive charge at the benzylic carbon atom, although the delocalization of the positive charge into the benzene ring is slightly smaller than that for protonation. This feature of the adduct ion with Me₃Ge⁺ resembles that for the Me₃Si⁺ adduct ions and is consistent with results obtained by theoretical calculations at the DFT B3LYP/6-31+G* level of theory.