Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The title problem has been investigated in two homologous series of positionally isomeric alkyltrimethylammonium salts, RCH₂CHXC₅H₁₁ and RCHXCH₂C₅H₁₁ (R = H, CH₃, C₂H₅, n-C₃H₇, iso-C₃H₇ and tert-C₄H₉; X = N⁽⁺⁾(CH₃)₃Cl)^(-), employing potassium tert-butoxide in tert-butanol and also potassium methoxide in methanol as the base-solvent combination. The overall rate constants of the individual olefin-isomer formation have been determined in these series and dissected, approximately, into the syn- and anti-components. The alkyl structure-reactivity relationship is thus obtained separately for the two complementary mechanisms of bimolecular elimination. The long-standing question whether steric or polar influence of alkyl group dominates in the complex reaction is re-examined on these grounds. Contrary to earlier extreme views it is shown that both the steric as well as the polar effects are very important, the former being operative mainly in the stereochemical (syn-anti) whereas the latter in the orientational (Hofmann-Saytzeff) control of the dichotomous reaction.