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37Cl/35Cl isotope effects in 13C NMR spectroscopy of chlorohydrocarbons

✍ Scribed by Abil E. Aliev; Kenneth D. M. Harris

Publisher
John Wiley and Sons
Year
1993
Tongue
English
Weight
375 KB
Volume
31
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Isotope effects on the chemical shift of ^13^C directly bonded to the isotopes ^35^Cl and ^37^Cl are reported for a wide range of chlorohydrocarbons. By recording ^13^C NMR spectra under conditions of composite pulse ^1^H decoupling, ^13^C resonances can be obtained that are sufficiently narrow to allow the very small splittings of the order of a few ppb due to the ^35^Cl/^37^Cl isotope effect to be resolved at ambient temperature. Observation of this phenomenon allows the routine identification of ^13^C resonances due to carbon atoms directly bonded to chlorine, since, for natural abundance samples, the isotope effect splits the ^13^C signal into a set of lines with a characteristic intensity distribution. Various structural features influencing the magnitude of the isotope effect have been elucidated, and the temperature dependence of the isotope effect is also discussed. From low‐temperature ^13^C NMR spectra for chlorocyclohexane, isotope shifts for the carbon atom directly bonded to chlorine were measured separately for the axial and equatorial conformations. The measured values indicate that the isotope shift is larger for the axial conformation.

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