Abstract:
In order to investigate the existence form for seven frequently used flavors which may make keto-enol tautomerism,their structures and transition states are calculated at B3LYP/6-311++G (2d,2p) level in both gas and water phase respectively.Meanwhile,the single point energies are calculated at MP2/6-311++G (2d,2p)∥B3LYP/6-311++G (2d,2p) level.The calculation results show that the activation energies for transition state of methylcyclopentenolone,3,4-dimethyl-1,2-cyclopentadione,1-methyl-2,3-cyclohexadione,4-hydroxy-2,5-dimethyl-3(2H)-furanone and maltol are too high to proceed keto-enol tautomerizm at room temperature even when catalyzed by water.The relative energies of the enol forms for the five substances are lower than their keto forms.As for 2,3-diketobutane and α-angelicalactone,they can make keto-enol tautomerizm when catalyzed by water at room temperature.And the relative energies of the keto forms for the two flavors are lower than their enol forms.The activation energy of the eight-membered ring transition state for seven compounds,which involving two water molecules for keto-enol tautomerism,are all significantly lower than those of no water catalyzed four-membered ring and those of one water molecule catalyzed six-membered ring transition state.