Selective photo-transformations in constrained media and theoretical investigation of the excited state nature of acetophenones
Description
The dissertation concentrates on two different topics, one the role of confined media in achieving selectivity in photoreactions and the other is the use of theoretical calculations to understand and gain insight into the experimental observations made on the photophysics in a constrained media Chapter 1 presents the concept of selectivity and the role of constrained media in achieving it and gives a general introduction about the structure and properties of zeolites. The chapter also brings out the potential of zeolites as a photochemical medium and the role it plays as a constrained and organized medium to effect selective photo-transformations Chapter 2 describes the use of zeolites in achieving regioselectivity in the singlet oxygen mediated photooxidation of simple alkenes. Cycloalkenes were chosen for the purpose of study and thionine adsorbed Y zeolites was used as the sensitizer/medium. The chapter discusses about the selectivity and complexity involved in the photooxidation and the fate of the dyes inside the zeolites on exposure to light. It also describes the various models put forward to explain the regiochemistry during the photooxidation which is unlike the solution chemistry Chapter 3 presents the use of zeolites in chiral photochemistry of aryl alkyl ketones. Chiral inductors are adsorbed onto the zeolite to render it chiral. The strategy of employing a reaction which uses one of the reactants to serve both as a reagent and as a chiral inductor has been shown. Remarkable enantioselectivities have been achieved for a photochemical process. A variety of chiral inductors and ketones have been scanned to understand the necessary interactions involved in the chiral induction. Tentative models have been proposed to understand the observed chiral chemistry Chapter 4 brings out the potential of another chiral medium called cyclodextrins. 4pi-photoelectrocyclization of pyridones was chosen for the study. The chapter describes the failure of conventional complexation procedure for water-soluble compounds like pyridones and the use of a new complexation procedure which gave good enantioselectivity. It also highlights the solvent free synthesis giving good enantioselectivities in the beta-lactam products and a crude model to understand the chiral induction by beta-cyclodextrin Chapter 5 describes the theoretical effort in supporting the experimental observations on the switch in the nature of the excited triplet state of aromatic ketones like acetophenone and 4'-methoxyacetophenone. It describes the success achieved with TD-DFT/6-31+G* and B3LYP/6-31G* methods and the failure of CIS calculations. The chapter discusses about the various binding modes of these ketones with alkali metal cations like lithium or sodium and changes observed in the lowest triplet excited state of aromatic ketone on binding to the cations