Physical organic chemistry studies of the dimethyldioxirane oxygen atom carbon-hydrogen bond insertion and epoxidation reactions.

摘要

The mechanistic aspects of the unactivated C-H bond oxygen atom insertion reaction by dimethyldioxirane are the main focus of this thesis. Both the relative reaction rates of C-H bond insertion reaction in an aromatic system and the absolute reaction rate of C-H bond insertion in an aliphatic system have been measured. The Hammett LFER plots for the aromatic system showed reaction constants of {dollar}rho{dollar} and {dollar}rhosp+{dollar} equal to {dollar}-{dollar}2.756 and {dollar}-{dollar}1.609, respectively. The LFER plots for the aliphatic system study showed the reaction constants {dollar}rhosb{lcub}rm I{rcub}{dollar}, {dollar}rhosbsp{lcub}rm I{rcub}{lcub}rm q{rcub}{dollar}, and {dollar}rhosp*{dollar} equal to {dollar}-{dollar}2.331, {dollar}-{dollar}0.406 and {dollar}-{dollar}1.043, respectively. These experimental results indicate that the C-H bond oxygen insertion reaction by dimethyldioxirane is electrophilic in nature.; The special effect of the -COOH and -OH groups on the C-H bond oxygen insertion reaction have been studied. Analyses of the changes of the reaction rates support the proposal that H-bonding between the -OH group and the DMD is responsible for the rate acceleration. The results also revealed that the lowest conformational energy of the substrate in the activated complex with DMD can be achieved by forming an H-bond between the -OH group and DMD. A solvent effect study for the C-H bond insertion reaction indicated that hydrogen bond donor (HBD) solvents accelerate the reaction rate.; The results of kinetic study for DMD epoxidation reaction of a series of substrates which contain a terminal C=C and a tertiary -OH demonstrate that H-bonding has a less pronounced effect on the rate of DMD epoxidation reactions. The non-equal diastereoisomer ratio of the products formed in the epoxidation reaction suggest that the H-bonding might also influence a facial preference for the DMD attack on the C=C double.; The results of the computational chemistry studies agree with the experimental finding that the DMD C-H bond insertion reaction is an electrophilic reaction, with no large extent of positive charge developed at the tertiary C center. Furthermore, the calculations predict that the C-H bond insertion reaction is a concerted, electrophilic reaction process.