Nitrogen-15 Isotope Effects in Bond Formation Reactions

Abstract

Nltrogen-15 isotope effects have been measured In the simple bond formation reactions of triethylamine with methyl iodide, triethylamine with ethyl iodide and triethylamine with ethyl bromide. Tests have been performed, to establish that the reactions were unidirectional under the experimental conditions and that the chemical procedures used to convert the quaternary ammonium salts to molecular nitrogen proceeded quantitatively. The mass spectrometer data were examined by rigorous statistical tests. At 6°C. the values of the ratio of rate constants, k14/k15, were: triethylamine-methyl iodide, 1.0009 +/- 0.0005; triethylamine-ethyl iodide, 1.0007 ±0.0006; trimethylamine-ethyl bromide, 0.9994 ±0.0006. For the reaction of triethylamine with ethyl iodide the value of k14/k15 increased slightly with increasing temperature. The results have been discussed in terms of the Bigeleisen theory of isotope effects with particular reference to the correct form for the effective mass term.