10.1021/jp983514h.s001 Michael J. Raiti Michael J. Raiti Michael D. Sevilla Michael D. Sevilla Density Functional Theory Investigation of the Electronic Structure and Spin Density Distribution in Peroxyl Radicals American Chemical Society 1999 terminal peroxyl oxygen atom CH lipid peroxyl radicals show 17 O peroxyl radicals density distribution ROO peroxyl group results Density Functional Theory Investigation Spin Density Distribution butyl peroxyl radicals 17 O hfcc Thiyl peroxyl radicals vinyl peroxyl radicals UHF DFT Spin density distributions SOO electron pair donor B 3LYP level methyl peroxyl radicals 1999-03-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Density_Functional_Theory_Investigation_of_the_Electronic_Structure_and_Spin_Density_Distribution_in_Peroxyl_Radicals/3727398 The 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 <i>tert</i>-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 <sup>17</sup>O hfcc's [<i>A</i><sub>∥</sub>(<sup>17</sup>O)] 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 <i>A</i><sub>∥</sub>(<sup>17</sup>O) 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. <i>A</i><sub>∥</sub>(<sup>17</sup>O) values for the terminal peroxyl oxygen atom correlate well with Taft σ* substitutent parameters for the R group in the peroxyl radicals (ROO<sup>•</sup>). 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 CH<sub>3</sub>SOO<sup>•</sup> 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.