Short-Lived Intermediates. 8. Excited States, Regioselectivity, and Stereospecificity in the Photochemistry of (R,S:S,R)- and (R,R:S,S)-1,2-Dimethylbutyl Trifluoroacetate

Article abstract of DOI:10.1021/ja00529a048

An investigation into the details of the type II photoelimination reaction in racemic (R,S:S,R)- (1a) and racemic (R,R:S,S)-1,2-dimethylbutyl trifluoroacetate (1b) in dodecane solution is presented and contrasted with similar studies of ketones.Stepwise statistical data extraction from quenching (1-dodecene) experiments gave the triplet excited state lifetimes (1a, 0.4; 1b, 2.1 ns), the fraction of reaction from each excited state giving alkene 2 (1a, 77 +/- 8percent singlet; 1b, 78 +/- 2percent singlet) and alkene 3 (1a, 76 +/- 5percent singlet; 1b, 76 +/- 6percent singlet), the regioselectivities of the singlet excited states (1a, 7.4 +/- 0.2; 1b, 4.3 +/- 0.1) and triplet excited states (1a, 6.6 +/- 0.9; 1b, 3.5 +/- 0.6), and stereospecificities of the singlet excited states (1a, 0.88 +/- 0.02; 1b, 0.74 +/- 0.01) and triplet excited states (1a, 0.59 +/- 0.10; 1b, 0.02 +/- 0.11).Dual quenching experiments gave singlet excited state lifetimes (1a, 2.6; 1b, 2.8 ns).The ester type II photoelimination reaction was shown to be markedly similar to analogous reactions in ketones.