The kinetics of Z/E isomerization of methyl oleate catalyzed by photogenerated thiyl radicals.
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.
Chatgilialoglu
Chryssostomos
C
ISOF Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy. chrys@isof.crn.it
Samadi
Abdelouahid
A
Guerra
Maurizio
M
Fischer
Hanns
H