Gas-Phase Acidities and O−H Bond Dissociation Enthalpies of Phenol, 3-Methylphenol, 2,4,6-Trimethylphenol, and Ethanoic Acid

Abstract

Energy-resolved, competitive threshold collision-induced dissociation (TCID) methods are used to measure the gas-phase acidities of phenol, 3-methylphenol, 2,4,6-trimethylphenol, and ethanoic acid relative to hydrogen cyanide, hydrogen sulfide, and the hydroperoxyl radical using guided ion beam tandem mass spectrometry. The gas-phase acidities of Δ_acidH₂₉₈(C₆H₅OH) = 1456 ± 4 kJ/mol, Δ_acidH₂₉₈(3-CH₃C₆H₄OH) = 1457 ± 5 kJ/mol, Δ_acidH₂₉₈(2,4,6-(CH₃)₃C₆H₂OH) = 1456 ± 4 kJ/mol, and Δ_acidH₂₉₈(CH₃COOH) = 1457 ± 6 kJ/mol are determined. The O−H bond dissociation enthalpy of D₂₉₈(C₆H₅O−H) = 361 ± 4 kJ/mol is derived using the previously published experimental electron affinity for C₆H₅O, and thermochemical values for the other species are reported. A comparison of the new TCID values with both experimental and theoretical values from the literature is presented.