Use of semiempirical AM1 calculations for the prediction of proton electron spin resonance spectra

Abstract

For Me _nX radicals (X = C˙, N˙, N⁺˙, O˙, O⁺˙, or S⁺˙), propanal cation radical, and biacetyl anion radical, quarter-annihilated hydrogen 1s spin densities obtained by semiempirical AM1-UHF quantum mechanical calculations are successfully converted into e.s.r. splitting constants for both α- and β-CH by multiplying by 1 177 G. This procedure produces splittings which range from –23 to + 135 G, with a correlation coefficient of 0.999 when plotted against the observed splittings, and an average deviation of 1.1 G. The temperature dependence of n-propyl and isobutyl radical β-splittings is well reproduced by these calculations. Allyl, benzyl, and phenoxyl radical calculations have too much spin contamination even after quarter annihilation for successful calculation of their e.s.r. spectra. The spin density calculations are poor for γ- but probably fairly good for δ-hydrogen atoms.