CNDO/2 CALCULATIONS ON ACIDITIES OF ALKANES AND SATURATED ALCOHOLS AND BASICITIES OF METHYLAMINES

The CNDO/2 method is applied to calculation of the energetics of (1) proton loss from alkanes and saturated alcohols forming the derived carbanions and alkoxide anions and (2) protonation of ammonia and methylated amines forming the derived ammonium salts. Alkane acidities are calculated to be opposite to the inductive order observed in solution. The orders of gas phase acidities of alcohols and basicities of methylamines are reproduced by the calculations in good agreement with experiment. It is proposed that the gas phase order of alkane acidities may be in agreement with the calculations, with the order in solution inverted by solvent effects as seems to be the case for the alcohol series. The calculations indicate the ability of alkyl groups to stabilize negative charge. The stabilities of alkyl carbanions and alkoxide anions directly correlate with the calculated delocalization of charge from the electronegative carbanion carbon or from the alkoxide oxygen. The larger or more complex the alkyl group, the greater the negative charge stabilization. Stabilization proceeds through the increase in alkyl group polarizability with increasing size or complexity. This is in contrast to alkyl group stabilization of positive charge in carbonium ions which seems to proceed through a conjugative interaction,. © 1969.