Theoretical Calculations of the Proton Affinities of <i>n</i>-Alkylamines, <i>n</i>-Alkyl Thiols, and <i>n</i>-Alcohols and the Ammonium Affinities of the <i>n</i>-Alcohols

Abstract

The B3LYP/6-31+G(d,p) method was used to calculate the proton affinities of n-alkylamines, n-alkyl thiols, and n-alcohols and the ammonium affinities of the n-alcohols up to C-18. These affinities and the gas-phase acidities of the n-alcohols were all found to correlate linearly with the quotient n/(n + 1), where n is the number of carbon atoms in the alkyl chain. This correlation leads to a limiting value of ΔH for very long alkyl chains: for the amines, thiols, and alcohols, the calculated maximum proton affinities PA298,max(RX) were 938.7, 828.2, and 816.9 kJ mol-1, respectively. The maximum ammonium affinity, −ΔH298,max, of the n-alcohols is 115.1 kJ mol-1.