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Title: Ab initio studies of hydrocarbon peroxyl radicals

Abstract

Extensive ab initio molecular orbital calculations have been performed for the importance series of peroxyl radicals (O/sub 2//sup .-/), HO/sub 2//sup ./, CH/sub 3/O/sub 2//sup ./, (CH/sub 3/)/sub 2/CHO/sub 2//sup ./, and (CH/sub 3/CH/sub 2/)/sub 2/CHO/sub 2//sup ./. Parameters calculated include equilibrium geometries, harmonic vibrational frequencies, dipole moments, and isotropic and anisotropic hyperfine couplings. Equilibrium geometries were of primary interest. In the two large hydrocarbon peroxyl radicals the carbon atoms and appropriate hydrogen atoms were constrained to be coplanar and the O-O group was forced to be perpendicular to the carbon chain in order to stimulate the presence of a peroxyl radical site in a polyethylene chain. Calculations were performed with large Gaussian basis sets (up to 6-311 ++G(d,p)). Calculations for HO/sub 2//sup ./ including electron correlation utilizing Moeller-Plesset perturbation theory were performed at the following levels: MP2(6-31G(d)) and 6-311G(d,p), MP3(6-311G(d,p)) and MP4SDTQ(6-311(d,p)). Calculated values are compared against the highly accurate experimental data for HO/sub 2//sup ./ known from microwave, laser magnetic resonance, and diode laser studies in order to determine the level of calculation necessary for accurate predictions. Comparison of the various calculations shows that MP2(6-31G(d)) compares favorably with MP4SDTQ(6-311G(d,p)) at a considerable savings in computation time.

Authors:
; ;
Publication Date:
Research Org.:
Oakland Univ., Rochester, MI
OSTI Identifier:
6953033
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem.; (United States); Journal Volume: 90:24
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; ORGANIC COMPOUNDS; HYPERFINE STRUCTURE; MOLECULAR STRUCTURE; PEROXY RADICALS; COUPLING; DIPOLE MOMENTS; MOLECULAR ORBITAL METHOD; PERTURBATION THEORY; THEORETICAL DATA; VIBRATIONAL STATES; DATA; ENERGY LEVELS; EXCITED STATES; INFORMATION; NUMERICAL DATA; RADICALS; 400201* - Chemical & Physicochemical Properties; 500200 - Environment, Atmospheric- Chemicals Monitoring & Transport- (-1989)

Citation Formats

Besler, B.H., Sevilla, M.D., and MacNeille, P.. Ab initio studies of hydrocarbon peroxyl radicals. United States: N. p., 1986. Web. doi:10.1021/j100282a009.
Besler, B.H., Sevilla, M.D., & MacNeille, P.. Ab initio studies of hydrocarbon peroxyl radicals. United States. doi:10.1021/j100282a009.
Besler, B.H., Sevilla, M.D., and MacNeille, P.. 1986. "Ab initio studies of hydrocarbon peroxyl radicals". United States. doi:10.1021/j100282a009.
@article{osti_6953033,
title = {Ab initio studies of hydrocarbon peroxyl radicals},
author = {Besler, B.H. and Sevilla, M.D. and MacNeille, P.},
abstractNote = {Extensive ab initio molecular orbital calculations have been performed for the importance series of peroxyl radicals (O/sub 2//sup .-/), HO/sub 2//sup ./, CH/sub 3/O/sub 2//sup ./, (CH/sub 3/)/sub 2/CHO/sub 2//sup ./, and (CH/sub 3/CH/sub 2/)/sub 2/CHO/sub 2//sup ./. Parameters calculated include equilibrium geometries, harmonic vibrational frequencies, dipole moments, and isotropic and anisotropic hyperfine couplings. Equilibrium geometries were of primary interest. In the two large hydrocarbon peroxyl radicals the carbon atoms and appropriate hydrogen atoms were constrained to be coplanar and the O-O group was forced to be perpendicular to the carbon chain in order to stimulate the presence of a peroxyl radical site in a polyethylene chain. Calculations were performed with large Gaussian basis sets (up to 6-311 ++G(d,p)). Calculations for HO/sub 2//sup ./ including electron correlation utilizing Moeller-Plesset perturbation theory were performed at the following levels: MP2(6-31G(d)) and 6-311G(d,p), MP3(6-311G(d,p)) and MP4SDTQ(6-311(d,p)). Calculated values are compared against the highly accurate experimental data for HO/sub 2//sup ./ known from microwave, laser magnetic resonance, and diode laser studies in order to determine the level of calculation necessary for accurate predictions. Comparison of the various calculations shows that MP2(6-31G(d)) compares favorably with MP4SDTQ(6-311G(d,p)) at a considerable savings in computation time.},
doi = {10.1021/j100282a009},
journal = {J. Phys. Chem.; (United States)},
number = ,
volume = 90:24,
place = {United States},
year = 1986,
month =
}
  • In this work we present an electron spin resonance investigation of the irradiation of the alkyl mercaptans methyl, n-butyl, and tert-butyl mercaptan and the radioprotective thiols cysteamine and dithiothreitol in a number of aqueous and organic matrices in the present of oxygen. Matrix peroxyl radicals (ROO*) are formed after the irradiation of organic matrices in the presence of oxygen at 77 K. Upon annealing, these react with added thiols to form sulfinyl radicals (RSO*). Evidence for a thiol peroxyl radical (RSOO*) intermediate is found. Hyperfine couplings and g values are reported for the sulfinyl radicals formed from the five thiolsmore » investigated. The incorporation of {sup 17}O-labeled oxygen into the RSO* radical confirms that molecular oxygen is the source of the oxygen atom in the radical. The isotropic and parallel anisotropic {sup 17}O couplings indicate slightly less than 0.5 spin density on the oxygen. The couplings and spin densities are compared to those predicted from ab inito molecular orbital calculations for CH{sub 3}SO*. Calculations for the sulfur-peroxyl intermediate, CH{sub 3}SOO*, predict that it will have similar ESR parameters as those predicted for the carbon-centered peroxyl radical, CH{sub 3}OO*.« less
  • The abstract for this journal is not available at this time.
  • An earlier calculation of hydrocarbon radical hyperfine coupling constants, using the spin-projected unrestricted Hartree Fock (PuHF) method is updated. Unprojected uHF calculations are performed for all the systems studied before. (AIP)
  • Ab initio calculations are reported for the isotropic hyperfine coupling constants arising from contact spin density distributions in hydrocarbon radicals. Representative sigma radicals (vinyl and ethynyl), nonconjugated pi radicals (methyl and ethyl), and conjugated pi radicals (allyl and cyclohexadienyl) are examined in the unrestricted Hartree-Fock approximation with a wide variety of Gaussian basis sets, ranging from crude minimal sets to a large uncontracted set. The unrestricted Hartree--Fock method itself gives poor results for this property, but is found to yield results of semiquantitative accuracy after a spin projection is performed. Some significant differences are found between results after full quartetmore » annihilation and after complete spin projection. Due to a systematic cancellation of errors, the crude minimal STO-3G basis set gives generally better results than more sophisticated minimal basis sets. Extended basis sets give only a slight overall improvement on the STO-3G results. The standard contraction schemes for large Gaussian basis sets are found to be quite appropriate for spin density calculations. It is concluded that the projected unrestricted Hartree--Fock method can be a useful tool for study of spin density distributions in hydrocarbon radicals even when deployed with highly contracted Gaussian basis sets.« less
  • Absolute rate constants for the reactions of substituted methylperoxyl radicals with ascorbate, urate, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), and TMPD (N,N,N{prime},N{prime}-tetramethyl-p-phenylenediamine) have been determined by pulse radiolysis is different solvents. In water-alcohol or water-dioxane solutions, the rate constants for trihalomethylperoxyl radicals generally increase with increasing water content. The rate constant for reaction of CCl{sub 3}O{sub 2}{center dot} radicals with trolox was measured in water, MeOH, i-PrOH, t-BuOH, ethylene glycol, diethyl ether, dioxane, acetone, acetonitrile, formamide, dimethylformamide, pyridine, and CCl{sub 4}. The rate constants were found to correlate well with a two-parameter equation that includes the dielectric constant of the solvent and themore » coordinate covalency parameter, a measure of the proton-transfer basicity of the solvent. Kinetic isotope effects in H{sub 2}O/D{sub 2}O of about 2 and activation entropies of about -1o eu for reduction of RO{sub 2}{center dot} by the organic reductants indicate that electron transfer to the peroxyl radical is concerted with the transfer of proton from the solvent to the incipient hydroperoxide anion.« less