Proton affinities of two weakly bidentate molecules: 1,2-dimethoxyethane and methoxyacetone

The proton affinities (PA), of methoxyacetone and 1,2-dimethoxyethane have been determined by the kinetic method, using alkyl ethers and simple ketone s having established PA values as their proton bound partners. Both compoun ds show effects attributed to activation entropies acting against the targe t molecules' retaining the proton. The PA values determined in this study w ere, PA methoxyacetone = 846.5 +/- 2 kJ/mol; PA 1,2-dimethoxyethane = 845.5 +/- 2 kJ/mol, (which is considerably lower than the previously cited value , 858 kJ/mol). The PA of cyclopentanone was revised to 828 +/- 4 kJ/mol fro m its reference value of 824 kJ/mol. The present work showed that simple ke tones and ethers, whose PA values conveniently overlap, cannot indiscrimina tely be used as reference compounds; care must always be taken in the choic e of the proton bound partner (reference) molecule in kinetic method studie s. (C) 2001 Elsevier Science B.V.