Mj. Raiti et Md. Sevilla, Density functional theory investigation of the electronic structure and spin density distribution in peroxyl radicals, J PHYS CH A, 103(11), 1999, pp. 1619-1626
The electronic structure and spin density distribution of peroxyl radicals
are investigated by density functional theory (DET) at the B3LYP level. Res
ults found for superoxide anion and tert-butyl peroxyl radicals at a variet
y of basis sets suggest that 6-31G is the most appropriate basis set for ca
lculation of hyperfine coupling constants (hfcc's) of carbon-based peroxyl
radicals. Calculation of parallel O-17 hfcc's [A(parallel to)(O-17)] for a
series of substituted methyl peroxyl radicals with the 6-31G basis set yiel
ded calculated values with a maximum deviation of 2.2% from experiment. Spi
n density distributions estimated from experiment A(parallel to)(O-17) are
compared to theoretical estimates from Mulliken orbital population analysis
. Electronegative substitution at the carbon alpha to the peroxyl group res
ults 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(parallel to
)(O-17) values for the terminal peroxyl oxygen atom correlate well with Taf
t sigma* substitutent parameters for the R group in the peroxyl radicals (R
OO.). Thiyl peroxyl radicals are reinvestigated using B3LYP for comparison
to previous theoretical work at UHF level. This resulted in confirmation th
at 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. Str
uctural models of lipid peroxyl radicals show that vinyl peroxyl radicals m
ay be distinguished from saturated, allylic, and ester-based peroxyl radica
ls on the basis of hyperfine coupling constants.