Density functional theory investigation of the electronic structure and spin density distribution in peroxyl radicals

Citation
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
Citations number
27
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
10895639 → ACNP
Volume
103
Issue
11
Year of publication
1999
Pages
1619 - 1626
Database
ISI
SICI code
1089-5639(19990318)103:11<1619:DFTIOT>2.0.ZU;2-3
Abstract
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.