Photoelectron Spectroscopy of Anilinide and Acidity of Aniline

Abstract

The photoelectron spectrum of the anilinide ion has been measured. The spectrum exhibits a vibrational progression of the CCC in-plane bending mode of the anilino radical in its electronic ground state. The observed fundamental frequency is 524 ± 10 cm^–1. The electron affinity (EA) of the radical is determined to be 1.607 ± 0.004 eV. The EA value is combined with the N–H bond dissociation energy of aniline in a negative ion thermochemical cycle to derive the deprotonation enthalpy of aniline at 0 K; Δ_acid<i>H</i>₀(PhHN–H) = 1535.4 ± 0.7 kJ mol^–1. Temperature corrections are made to obtain the corresponding value at 298 K and the gas-phase acidity; Δ_acid<i>H</i>₂₉₈(PhHN–H) = 1540.8 ± 1.0 kJ mol^–1 and Δ_acid<i>G</i>₂₉₈(PhHN–H) = 1509.2 ± 1.5 kJ mol^–1, respectively. The compatibility of this value in the acidity scale that is currently available is examined by utilizing the acidity of acetaldehyde as a reference