Hydrogen isotope fractionation factors for N,N-dimethylbenzylammonium ion and some related species: an unusually strong preference for deuterium over protium
作者:Hong-Xun Guo、A. Jerry Kresge
DOI:10.1039/a604674f
日期:——
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.
重氢分馏因子通过 1H 和 13C NMR 方法在水溶液中测定,结果为 PhCH2NLMe2+ (ϕ = 1.47 ± 0.05)、PhCH2OL (ϕ = 1.04 ± 0.06)、PhCO2L (ϕ = 1.04 ± 0.08) 和 CH3CO2L (ϕ = 0.99 ± 0.02)。将 PhCH2NMe2 从 H2O 转移到 D2O 的介质效应也通过将该物质分配在水和不混溶的有机溶剂中确定,结果为 ϕ = 1.025 ± 0.003。此外,采用 UV 光谱法测量了溶剂同位素效应对 PhCH2NLMe2+ 酸离解的影响,结果为 (Qa)H/(Qa)D = 4.88 ± 0.16。这一溶剂同位素效应与使用相关分馏因子预测的值 (Qa)H/(Qa)D = 4.38 ± 0.28 非常接近。PhCH2NLMe2+ 的异常大的 ϕ 值归因于由于离子的四面体结构和其甲基团的体积所导致的 N–L 键的弯曲振动变得更加刚性。