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DOI: 10.1039/A604674F (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1997, 295-298

Hydrogen isotope fractionation factors for N,N-dimethylbenzylammonium ion and some related species: an unusually strong preference for deuterium over protium

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Hong-Xun Guo and A. Jerry Kresge

Abstract

Deuterium fractionation factors were determined by the 1H and 13C NMR methods in aqueous solution for PhCH2NLMe2+ (ϕ = 1.47 ± 0.05), PhCH2OL (ϕ = 1.04 ± 0.06), PhCO2L (ϕ = 1.04 ± 0.08), and CH3CO2L (ϕ = 0.99 ± 0.02). The medium effect for transferring PhCH2NMe2 from H2O to D2O, ϕ = 1.025 ± 0.003, was also determined by partitioning this substance between water and immiscible organic solvents, and a UV spectroscopic method was used to measure the solvent isotope effect on the acid ionization of PhCH2NLMe2+, (Qa)H/(Qa)D = 4.88 ± 0.16. This solvent isotope effect agrees well with the value predicted using the relevant fractionation factors, (Qa)H/(Qa)D = 4.38 ± 0.28. The unusually large value of ϕ for PhCH2NLMe2+ is attributed to stiffened bending vibrations of its N–L bond imposed by the tetrahedral structure of the ion and the bulk of its methyl groups.

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