The basicity of substituted N,N‐dimethylanilines in solution and in the gas phase

Abstract

Basicities of a number of ring‐substituted N,N‐dimethylanilines (DMA) and some related bases in water, acetonitrile, and THF and in the gas phase have been experimentally determined. Gas‐phase basicities of DMAs and related bases were calculated at DFT B3LYP 6‐311+G** and G3(MP2) levels. Structure–Basicity relationships in these four media were discussed. By comparison of gas‐phase basicity shifts induced by stepwise substitution, starting from ammonia and ending at triphenylamine, it was observed that solvent effects of water and acetonitrile exceed the structural effects on intrinsic basicity. It was shown that the influence of substituents in the phenyl ring on DMA basicity is reduced by two to three times when going from the gas phase into the abovementioned condensed media. In the gas phase, 4‐NO, 4‐NO2, 4‐CN, 4‐COMe, and 4‐CHO substituted DMAs protonate on substituent, whereas in solvents, only 4‐NO‐DMA probably protonates on substituent. The sensitivity of DMA basicity toward substitution in the phenyl ring was compared with the related family of phenylphosphazene bases, and it was found that the substituent effect is stronger in DMAs by 1.35 times in acetonitrile, 1.45 times in the gas phase, 2.0 times in THF, and 2.6 times in water. Copyright © 2012 John Wiley & Sons, Ltd.