Estimation of ionization energies of substituted anilines by the kinetic method

Abstract

Ionization energy (IE) determinations by the kinetic method are extended to a functionalized class of compounds: substituted anilines. The radical-cation-bound dimers of substituted anilines were generated under self-CI conditions and the dissociation products examined using two collision energies, 2 and 10 eV, in a triple quadrupole tandem mass spectrometer. Using N, N-diethylaniline (IE = 6.98 ± 0.02 eV), 3,5-dimethylaniline (IE = 7.2 eV), N-methylaniline (IE = 7.33 ± 0.02 eV), 2-methylaniline (IE = 7.44 ± 0.02 eV), 3-methylaniline (IE = 7.50 ± 0.02 eV), aniline (IE = 7.720 ± 0.002 eV), and benzylamine (IE = 8.64 ± 0.05 eV) as reference compounds, a linear correlation is observed between the natural log of the ratio of the fragment ion abundances versus ionization energy for each collision energy. The effective temperature of the activated cluster ions rises from 1180 to 1470 K as the collision energy is raised from 2 to 10 eV. The average estimated IE values for 4-methoxyaniline, 2-methoxyaniline, 4-methylaniline, 3-chloroaniline and 3-fluoroaniline are determined to be 7.00 ± 0.15 eV, 7.19 ± 0.07 eV, 7.37 ± 0.07 eV, 8.27 ± 0.08 eV, 8.37 ± 0.07 eV respectively.