Structure-reactivity effects on primary deuterium isotope effects on protonation of ring-substituted alpha-methoxystyrenes.

ABSTRACT: Primary product isotope effects (PIEs) on L(+) and carboxylic acid catalyzed protonation of ring-substituted alpha-methoxystyrenes (X-1) to form oxocarbenium ions X-2(+) in 50/50 (v/v) HOH/DOD were calculated from the yields of the alpha-CH(3) and alpha-CH(2)D labeled ketone products, determined by (1)H NMR. A plot of PIE against reaction driving force shows a maximum PIE of 8.7 for protonation of 4-MeO-1 by Cl(2)CHCOOH (DeltaG(o) = 1.0 kcal/mol). The PIE decreases to 8.1 for protonation of 4-MeO-1 by L(3)O(+) (DeltaG(o) = -2.8 kcal/mol) and to 5.1 for protonation of 3,5-di-NO(2)-1 by MeOCH(2)COOH (DeltaG(o) = 13.1 kcal/mol). The PIE maximum is around DeltaG(o) = 0. Arrhenius-type plots of PIEs on protonation of 4-MeO-1 and 3,5-di-NO(2)-1 by L(3)O(+) and on protonation of X-1 by MeOCH(2)CO

SUBMITTER: Tsang WY 

PROVIDER: S-EPMC2825562 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature