Abstract:
The transfer of hydrogen atoms between molecules in the molecular complexes quinhydrone (Q-H
2Q) which consisted of benzoquinone(Q) and hydroquinone (H
2Q), is studied with MNDO(RHF, UHF). The first model (
pp) is the hydrogen atoms transfers take place between the two parallel molecular planes; the second model(
zz) is the transfers being through the hydrogen bond from H
2Q to Q which are keeping co-plane. The charge transfers, heat of formation and transientstate configurations are optimized for two processes:(A). 2H-transfer:Q-H
2Q+Q→Q+H
2Q, (B). 1H-transfer:H
2Q+Q→2HQ (semiquinone, have diamagnetic→paramagnetic). The 1H-transfer potential barrier of (q) is 5.2eV(ground state) and 5.5eV (triplet); but for (
pp), it is 2.5 and 3.0 respectively, the comparatively lower barrier is the fact that consistent with phenomenon that crystal quinhydrone from diamagnetic converted to paramagnetic when temperature above 100°. The barriers of 2H-transfer of (
pp) in ground state are 5.3eV(90°) and 7.9eV(112°), but in excited state they are 3.0eV(112°, singlet) and 3.5eV(112°,triplet). The cooperation effects have been obtained by calculations; in (
pp) model,when 1H-OR 2H-transfer from H
2Q to Q, the distances between the oxygen atoms can harmoniously shortened, then it is profit to the hydrogen transfer.