title: Beta-deuterium isotope effects on amine basicity, "inductive" and stereochemical.
abstract: Secondary beta deuterium isotope effects on acidity constants of ammonium ions are measured using a remarkably precise NMR titration method. Deuteration is found to increase the basicity of methylamine, dimethylamine, benzylamine, and N,N-dimethylaniline. The effect is attributed to a lowered zero-point energy of a CH bond adjacent to an amine nitrogen. The method permits a determination of the stereochemical dependence of the isotope effect in a locked piperidine, and it is found that deuteration is more effective when antiperiplanar to a lone pair. The values are consistent with a cos(2) dependence on dihedral angle, with no detectable angle-independent inductive effect.
authors.affiliation: Department of Chemistry 0358, University of California, San Diego, La Jolla, California 92093-0358, USA.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Perrin
authors.forename: Brian K
authors.initials: BK
authors.lastname: Ohta
authors.forename: Joshua
authors.initials: J
authors.lastname: Kuperman
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D000588:Amines / Q000737:chemistry*; D001596:Benzylamines / Q000737:chemistry; D041961:Deuterium Exchange Measurement; D004123:Dimethylamines / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008744:Methylamines / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000588:Amines; D001596:Benzylamines; D004123:Dimethylamines; D008744:Methylamines; C042294:N,N-dimethylalanine; C030796:benzylamine; C034516:dimethylamine; C027451:methylamine; D000409:Alanine