REMOTE SECONDARY DEUTERIUM KINETIC ISOTOPE EFFECTS AS A PROBE OF STERIC STRAIN IN THE SOLVOLYSIS OF TERTIARY ALKYL CARBINYL SYSTEMS

The kinetic isotope effects associated with the solvolysis of 9-tert-butyl-9-bicyclo[3.3.1 ]nonyi (3), 2-tert-butyl-2-adamantyl (4), and 2-tert-butyl-endo-camphenilyl (5) p-nitrobenzoates, completely deuterated at the ferr-butyl groups, were found in 95.6% aqueous ethanol at 25 °C to be (kH/kD =) 1 -030, 1.107, and 1.076, respectively. Compound 3 gave primarily unrearranged alcohol (7.7%) and the methyl-shifted alkene 9-(2ʹ-propenyl)-9-methylbicyclo[3.3.1 ]nonane (88.4%) as solvolysis products. A preference for CH3 migration over CD3migration by a factor of 1.35 was observed. Compound 4 similarly yielded unrearranged alcohol (6.9%) and the methyl-shifted alkene 2-(2-ʹpropenyl)-2-methyladamantane (90.2%) and showed a preference for CH3 over CD3migration in product formation by a factor of 1.25. The kinetic isotope effects are interpreted in terms of relief of constraints on vibrational freedom at the positions of isotopic substitution during the activation process. The kinetic isotope effects did not correlate well with the f-Bu/CH3 substituent effects. © 1979, American Chemical Society. All rights reserved.