Kinetic hydrogen isotope effects in the thermal decomposition of t-butyl N-p-tolylcarbamates

Abstract

Kinetic isotope effects for the thermal decomposition of t-butyl-, [²H₃]t-butyl-, [²H₆]t-butyl-, and [²H₉]t-butyl-N-p-tolylcarbamates have been determined in the range 473 ± 10 K. Multiple isotopic substitution leads to almost cumulative effects with k_H : k_D per CD₃ca. 1.31, indicating that these are secondary rather than primary isotope effects. Hyperconjugation of the CH₃ groups with the forming partial positive charge at the α-carbon atom is considered to be the major source of the isotope effects.