The design of fast radical clocks and determination of their rate constants through ester photochemistry

摘要

Using laser flash photolysis, the rate constants for reactions of intermediates generated in photochemical reactions can be determined directly. In many cases, however, direct measurement is not possible, and instead, the rate constants are determined by comparison with the rate constant of a known radical reaction. These "radical clocks" cover a wide range of rates even into the picosecond range. Results on the photochemistry of esters indicate that rate constants for both electron transfer converting the radical pair to the ion pair and rate constants of decarboxylation of the acyloxy radical are in the 10$sp9$ to 10$sp{11}$ s$sp{-1}$ range. The rate constants of $beta$-cleavage which, based on previous work by Wagner, are in the range of $sim$10$sp8$ s$sp{-1}$ depending on the group, X, can be used to further calibrate the rate constants of electron transfer and decarboxylation.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE MAI)The photochemistry of the ester (N = 1-naphthyl) for X = Br has been studied. Future studies will include X = -SO-Ph-CH$sb3$, -SO-CH$sb3$, and the phenyl cyclopropyl naphthylmethyl radical, 1. The latter is believed to have a rate constant of ring-opening in the same range as the $beta$-cleavage reaction.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE MAI).