HYDROGEN ISOTOPE FRACTIONATION FACTORS FOR N,N-DIMETHYLBENZYL-AMMONIUM ION AND SOME RELATED SPECIES - AN UNUSUALLY STRONG PREFERENCE FOR DEUTERIUM OVER PROTIUM

Deuterium fractionation factors were determined by the H-1 and C-13 NM R methods in aqueous solution for PhCH(2)NLMe(2)(+) (phi = 1.47 +/- 0. 05), PhCH(2)OL (phi = 1.04 +/- 0.06), PhCO(2)L (phi = 1.04 +/- 0.08), and CH(3)CO(2)L (phi = 0.99 +/- 0.02), The medium effect for transferr ing PhCH(2)NMe(2) from H2O to D2O, Phi = 1.025 +/- 0.003, was also det ermined by partitioning this substance between water and immiscible or ganic solvents, and a UV spectroscopic method was used to measure the solvent isotope effect on the acid ionization of PhCH(2)NLMe(2)(+), (Q (a))(H)/(Q(a))(D) = 4.88 +/- 0.16, This solvent isotope effect agrees well with the value predicted using the relevant fractionation factors , (Q(a))(H)/(Q(a))(D) = 4.38 +/- 0.28, The unusually large value of ph i for PhCH(2)NLMe(2)(+) is attributed to stiffened bending vibrations of its N-L bond imposed by the tetrahedral structure of the ion and th e bulk of its methyl groups.