Chemistry International -- Newsmagazine for IUPAC

Common Values of Nuclear Electric Quadrupole Coupling Terms for Appropriate Nuclei in Functionalized Hydrocarbons

Numerous common functionalized hydrocarbon chains contain quadrupolar nuclei, I > ½, such as chlorine and nitrogen. These groups include halocarbons, acyl chlorides, nitriles, amines and amides. High resolution spectroscopy affords the measurement of nuclear electric quadrupole coupling constants for these nuclei within the molecule of interest. These constants are essentially the product of the nuclear electric quadrupole moment and the electric field gradient at the nuclei. The electric field gradient is informative for several reasons. First, the magnitude of the electric field gradient can be interpreted, via a simple model, in terms of the ionicity and/or hybridization of the bonding orbitals involving the quadrupolar nuclei. Second, these quantities can be directly linked to analogous values determined through nuclear magnetic resonance spectroscopy. Third, these “tight” quantities provide useful benchmark data for high-level computational chemistry methodologies.

We have already established that there are somewhat “standard” nuclear quadrupolar coupling constants for chlorine in various acyl chlorides χzz ~ -60 MHz, and furthermore, these values differ from the chlorine nuclear quadrupole coupling constants in perfluoroacyl chlorides, χzz ~ -65 MHz.

In this context, the task group for this project will scour the literature to determine more “standard” values. These data will be compiled, interpreted, and discussed.