The potential energy surfaces for the C-C, C-Br and C-Cl dissociations of BrCH 2 COCl(S 1 ) are investigated at the CAS(8,7)/6 31G * and MR CI/cc pVDZ levels of theory, which provides some new insights into the mechan...The potential energy surfaces for the C-C, C-Br and C-Cl dissociations of BrCH 2 COCl(S 1 ) are investigated at the CAS(8,7)/6 31G * and MR CI/cc pVDZ levels of theory, which provides some new insights into the mechanism of the BrCH 2 COCl photodis sociation at 248nm. It is found that the relative strength of the C-C and C-Cl α bonds is one of the factors that influence the selectivity of the α bond fissions. However, the selectivity is mainly determined by the mechanism of dissociation upon n→π * excitation. The preference of the C-Cl α bond fission over the C-Br β bond cleavage is attributed to the nonadiabatic recrossing in previous studies. The present calculations predict that distance dependence of intramolecular energy relaxation is another important factor that influences the selectivity of the α and β bond cleavages.展开更多
Arbutin was synthesized from glucose by two-step reaction below: (a) 2,3,4,6-tetra-O-acetyl-α-D-glucosyl chloride or bromide was prepared by glucose and acetyl halide (chloride or bromide), (b) 2,3,4,6-tetra-O-ace-t...Arbutin was synthesized from glucose by two-step reaction below: (a) 2,3,4,6-tetra-O-acetyl-α-D-glucosyl chloride or bromide was prepared by glucose and acetyl halide (chloride or bromide), (b) 2,3,4,6-tetra-O-ace-tyl-α-D-glucosyl halide (Cl, Br) reacted with hydroquinone, methanol as solvent at pH=9.5-10.0.展开更多
文摘The potential energy surfaces for the C-C, C-Br and C-Cl dissociations of BrCH 2 COCl(S 1 ) are investigated at the CAS(8,7)/6 31G * and MR CI/cc pVDZ levels of theory, which provides some new insights into the mechanism of the BrCH 2 COCl photodis sociation at 248nm. It is found that the relative strength of the C-C and C-Cl α bonds is one of the factors that influence the selectivity of the α bond fissions. However, the selectivity is mainly determined by the mechanism of dissociation upon n→π * excitation. The preference of the C-Cl α bond fission over the C-Br β bond cleavage is attributed to the nonadiabatic recrossing in previous studies. The present calculations predict that distance dependence of intramolecular energy relaxation is another important factor that influences the selectivity of the α and β bond cleavages.
文摘Arbutin was synthesized from glucose by two-step reaction below: (a) 2,3,4,6-tetra-O-acetyl-α-D-glucosyl chloride or bromide was prepared by glucose and acetyl halide (chloride or bromide), (b) 2,3,4,6-tetra-O-ace-tyl-α-D-glucosyl halide (Cl, Br) reacted with hydroquinone, methanol as solvent at pH=9.5-10.0.
