title: The kinetics of Z/E isomerization of methyl oleate catalyzed by photogenerated thiyl radicals.
abstract: The reaction of beta-mercaptoethanol with methyl oleate in tertbutyl alcohol was investigated under photochemical conditions. The time-dependent Z/E isomerization of the unsaturated moiety as well as the thiol-adduct formation were analyzed on the basis of radical generation rates and established rate constants. This provides precise room-temperature rate constants for the reversible thiyl radical addition to both Z and E isomers. The rate constants for HOCH2CH2S* addition to the Z and E forms were found to be 1.6 x 10(5) and 2.9 x 10(5) M(-1) S(-1), respectively. For the beta-elimination of the thiyl radical from the alkyl radical adduct, the rate constants were 1.7 x 10(7) and 1.6 x 10(8) S(-1), the faster associated with the formation of the E isomer. DFT-BB1K calculations on 2-butene assign this large preference of fragmentation for the E isomer to a lower activation barrier for the formation of the E transition state from the equilibrium radical adduct structure.
authors.affiliation: ISOF Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy. chrys@isof.crn.it
authors.forename: Chryssostomos
authors.initials: C
authors.lastname: Chatgilialoglu
authors.forename: Abdelouahid
authors.initials: A
authors.lastname: Samadi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Guerra
authors.forename: Hanns
authors.initials: H
authors.lastname: Fischer