Proton affinities of the hydrogen, methyl, and trifluoromethyl halides from pulsed electron beam high pressure mass spectrometric equilibria measurements

Abstract

Pulsed electron beam high pressure mass spectrometric techniques have been used to investigate proton transfer equilibria involving hydrogen and trifluoromethyl halides. Methyl cation transfer equilibria have also been used to determine methyl cation affinities of hydrogen halides. Proton affinities obtained are HCl = 137.5, HBr = 142.9, Hl = 150.9, CF3Cl = 139.0, CF3Br = 141.3, and CF3l = 150.4 kcal mol−1. Methyl cation affinities obtained are HF = 15 ± 2, HCl = 19.8, HBr = 21.3, and Hl = 31.1 kcal mol−1. The values of methyl cation affinity of hydrogen halides can in turn be used to calculate proton affinities of the methyl halides of CH3Cl = 160.8; CH3Br = 164.8; and CH3l = 171 kcal mol−1. Linear correlations are found between proton affinities and valence ionization potentials and between proton affinities and methyl cation affinities.