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Structural and thermochemical studies on CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, CH 3 SC(═O)CH 3, and radicals corresponding to loss of H atom
Author(s) -
Song Guanghui,
Bozzelli Joseph W.
Publication year - 2017
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3688
Subject(s) - chemistry , density functional theory , isodesmic reaction , ab initio , radical , standard enthalpy of formation , bond dissociation energy , molecule , computational chemistry , conformational isomerism , dissociation (chemistry) , organic chemistry
CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 are intermediates during the partial oxidation of CH 3 SCH 2 CH 3 in the atmosphere and in combustion processes. Thermochemical properties (ΔH f o , S o and C p (T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6‐311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH f o 298 ) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6‐31 + G(d,p) level calculations. The contributions for S o 298 and C p (T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer‐Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 are −34.6 ± 0.8, −42.4 ± 1.2, and ‐49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur‐containing compounds.