Thermochemical determinations by tandem mass spectrometry
Abstract
The kinetic method is applied to thermochemical determinations. The proton affinity, gas-phase basicity, and gas-phase acidity of urea are estimated to be 873.5 ± 5.0, 841.6 ± 5.0, and 1513.8 ± 12.0 kJ/mol, respectively. These values are found to be in good agreement with those obtained from G2(MP2) molecular orbital calculations. The electron affinities of dibenzo[a,g]corannulene (C28H14) and diindenochrysene (C26H 12) are determined as 1.00 ± 0.2 and 1.16 ± 0.2 eV, respectively. In analogous experiments, the electron affinities of C60 are calculated to be 1.20 ± 0.2 and 1.24 ± 0.2 eV, respectively. These values are significantly lower than the known value of 2.65 eV. This is explained as a “local” electron affinity of C60. The kinetic method is also applied, for the first time, in the determination of ionization energies (IE). The IE of 3-iodobenzonitrile is determined as 9.39 ± 0.5 eV. The kinetic method has also been extended to determine polyatomic cation affinities towards pyridines and to investigate the stereoelectronic effects arising from ortho-substitution on the pyridines. The cations studied include SiCl3+, SiCl+, (CH3O) 2B+, CH3OB+H, and PCl 2+. Remarkably good correlations are observed between the logarithm of the fragment ion abundance ratio and proton affinities of the meta- and para-substituted pyridines for each cation studied. Deviations from the linear correlations are observed for ortho-substituents and are attributed to a combination of agostic bonding and steric hindrance. Agostic bonding is three-center two-electron bonding (C-H-M+) which involves the C-H bond of the ortho-substituent and the central cation. The kinetic method is also applied to studied higher orders of clusters, such as Fe +-bound trimers and tetramers, which can be used to study molecular pair and molecular triplet Fe+ affinities.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry|Physical chemistry|Chemistry
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