Methyl-d3 isotope effects, .alpha.-methyl hydrogen rate effects, and the analysis of some solvolytic reaction mechanisms

Rate and Product Studies with 2-Methyl-2-Chloroadamantane under Solvolytic Conditions

“…ether (or 21% ~ 41% 2-methyl-2-adamantyl (2,2,2-trifluoro) ethyl ether), and 27% ~ 77% 2-methyl-2-adamantanol, respectively. These values are very similar to those previously observed by Shiner 14 and Bentley 12 and their co-worker. As expected, the amount of 2-methyl-2-adamantanol (2-Me-2-AdOH) increased with increasing water content of the solvent, and in aqueous ethanol and TFE-ethanol mixtures the amount of 2-methyleneadamantane (olefin) decreased with increasing the solvent ionizing power (YCl-value).…”

Determining transition state structure using kinetic isotope effects

“…For example, in carbenium ion S N reactions, the magnitude of the KIE is strongly dependent on the stereochemistry of the developing carbenium ion in the transition state. Shiner and coworkers 51,54,55 found that the magnitude of the KIE is reduced from 1.30/ b-D when the dihedral angle between the C b -H bond and the empty 2p atomic orbital on the a-carbon in the transition state is 08 to 1.07/ b-D when the dihedral angle is 308, to only 1.01/ b-D when the dihedral angle is 608 and is inverse at 0.99 when the dihedral angle is 908. This is not a serious problem, however, because small b-deuterium KIEs are only found in the carbenium ion reactions of bicyclic and other sterically crowded systems where free rotation about the C a -C b bonds is restricted.…”

Remote secondary deuterium kinetic isotope effects as a probe of steric strain in the solvolysis of tertiary alkyl carbinyl systems

“…34 For example, a linear free energy relationship between the logarithms of the a-CH3/H and a-CH3/CD3 rate ratios has been shown to exist by Shiner, Sunko, and co-workers for a number of solvolysis reactions. 35 This correlation is apparently a manifestation of the predominant importance of hyperconjugative interactions in both the methyl effect and the /3-deuterium kinetic isotope effect. Establishment of correlations of this type is useful, because deviations then become mechanistically significant.…”