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Density Functional Theory Investigation of the Electronic Structure and Spin Density Distribution in Peroxyl Radicals
journal contribution
posted on 1999-03-02, 00:00 authored by Michael J. Raiti, Michael D. SevillaThe electronic structure and spin density distribution of peroxyl radicals are investigated by density functional
theory (DFT) at the B3LYP level. Results found for superoxide anion and tert-butyl peroxyl radicals at a
variety of basis sets suggest that 6-31G is the most appropriate basis set for calculation of hyperfine coupling
constants (hfcc's) of carbon-based peroxyl radicals. Calculation of parallel 17O hfcc's [A∥(17O)] for a series of
substituted methyl peroxyl radicals with the 6-31G basis set yielded calculated values with a maximum deviation
of 2.2% from experiment. Spin density distributions estimated from experiment A∥(17O) are compared to
theoretical estimates from Mulliken orbital population analysis. Electronegative substitution at the carbon
alpha to the peroxyl group results in an increase of terminal oxygen hyperfine coupling and spin density,
shortening of C−O, and lengthening of O−O. In cases involving significant steric hindrance, however, C−O
bond shortening was prevented. A∥(17O) values for the terminal peroxyl oxygen atom correlate well with Taft
σ* substitutent parameters for the R group in the peroxyl radicals (ROO•). Thiyl peroxyl radicals are
reinvestigated using B3LYP for comparison to previous theoretical work at UHF level. This resulted in
confirmation that the effect of the addition of an electron pair donor (hydroxide ion) to CH3SOO• is to alter
the spin density distribution in the peroxyl group. Structural models of lipid peroxyl radicals show that vinyl
peroxyl radicals may be distinguished from saturated, allylic, and ester-based peroxyl radicals on the basis of
hyperfine coupling constants.
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terminal peroxyl oxygen atomCHlipid peroxyl radicals show17 Operoxyl radicalsdensity distributionROOperoxyl group resultsDensity Functional Theory InvestigationSpin Density Distributionbutyl peroxyl radicals17 O hfccThiyl peroxyl radicalsvinyl peroxyl radicalsUHFDFTSpin density distributionsSOOelectron pair donorB 3LYP levelmethyl peroxyl radicals
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