Cooperation Effects of Hydrogen Transfer In Quinhydrone Quantum Chemistry Study

The transfer of hydrogen atoms between molecules in the molecular complexes quinhydrone (Q-H₂Q) which consisted of benzoquinone(Q) and hydroquinone (H₂Q), 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 H₂Q 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-H₂Q+Q→Q+H₂Q, (B). 1H-transfer:H₂Q+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 H₂Q to Q, the distances between the oxygen atoms can harmoniously shortened, then it is profit to the hydrogen transfer.