Electron Spin Resonance and Electronic Structure of Triphenylmethyl^1,2

Abstract

The anisotropic hyperfine splitting due to C13 in the methyl position of triphenylmethyl has been obtained from dilute Analysis of the measurements yields an estimate of density of unpaired The A simple valence bond approximation is in good solutions of triphenylmethyl in triphenylamine. electron a t the methyl position. magnitudes of the densities require that some of them have negative sign.Estimates of densities a t other positions are made from proton hyperfine splittings. agreement with the observations.

Structure and dynamics of the lowest triplet state in p-benzoquinone

“…We then calculate † a value of 150 MHz for the carbon-13 hyperfine interaction constant per unit π spin-density. This number is in good agreement with the value of 156 MHz reported by Adam and Weissman [16] and some 15% higher than the value reported by Smith et al [17]. This latter value was recently used by us in a preliminary analysis of the carbon-13 ENDOR data [8].…”

“…The isotopically mixed crystals of PBQ were grown in a Bridgeman furnace and cleaved or cut with a sharp razorblade in the desired direction. 7-17 O-PBQ-h 4 was prepared through exchange of the 16 O-isotope with oxygen-17 enriched water (20%) in benzene, a procedure described by Becker et al [12]. The enrichment of 17 O in PBQ obtained, was found to be ca.…”

The electron spin resonance spectra of CH(SO3)2=and N(SO3)2=

“…The inconsistency in r is not too serious but the values of (r -a) vary by up to 35 per cent. Earlier discussions of laC anisotropic couplings [6,8,15,16,17] have been based on (r -3> values from Torrance [11] or Barnes and Smith [13] rather than Jucys [12] whose appreciably higher values are supported by the most recent figures of Mayers [14]. Since Mayers' values are obtained with the aid of modern computers and since his values for P, S and C1 proved consistent [1] with those of Watson and Freeman [18] they are to be preferred.…”

Spin density and spin correlation in triplet states

“…Cn ~ II (8) in which 2n electrons occupy the self-consistent orbitals r Cn. The excited triplet state is reached by exciting an electron from the occupied orbital Cm to the vacant one Cj, and its wave function is approximately ~Fo= I[ r Cm ~... Cn2r ~ II- (9) With the orbitals r 9 9 Cn as the starting point we could reach the extended Hartree-Fock wave function by an iterative solution of the self-consistent field equations.…”

“…spectra of oriented radicals in a single crystal [3] and on the nuclear magnetic resonance Knight shift of ring protons in radicals at low temperature [4,5] have directly demonstrated these 'negative spin densities '. They have also been inferred from the ring proton hyperfine structure of e.s.r, in alternant hydrocarbon radicals [6][7][8][9][10] and radical ions [9,11].…”