Journal of M olecular Structure, 104 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML (1983) 23- 35 THEOCHEM Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands zyxwvutsrqponmlkjihgf ELECTRIC FIELD GRADIENT AND FORCE CONSTANT IN NITRILES Y OSSLEN ARAY * and JUAN MURGICH* * Centro de Quimica, Instituto Venezolano de Inuestigaciones Cientificas (IVIC), Apartado 1827, Caracas 1010-A (Venezuela) (Received 15 July 1982) ABSTRACT The relationship between the principal component of the electric field gradient (eqN) and the stretching force constant (kCN) obtained by Salem for diatomic molecules is extended to polyatomic molecules with linear fragments of type R-C-N. It is found that for nitriles there is a linear correlation between kcN and cqN values, as predicted by theory, and that such correlation depends on the degree of conjugation between R and CN orbitals. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Many workers [l--5] have studied the relationship between the magni- tude of the vibrational force constant and the electronic charge distribution or related quantities such as the Electric Field Gradient (EFG). Salem [l] found for diatomic molecules that the stretching force constant (kcN) is related to the components of the EFG at the nuclear sites, plus a term related to the electronic charge density within the nuclei and a third term which describes the charge relaxation produced by the vibrational motion. The results of Salem led some workers to search for similar correlations between nuclear quadrupole resonance data and quantities related to force constants [ 6-91. One of the difficulties in these studies was the lack of a reliable set of force constants for the molecules under study. However, a method capable of calculating force constants with high accuracy was developed [ 10, 111 recently thus opening the possibility of detailed studies of the correlation between quantities such as the EFG components and force constants. In the present work we have extended the relationship between hcN and the principal component of the EFG (eqN) at the N nucleus found by Salem [l] for diatomics to polyatomic molecules containing linear fragments of the type R-C-N. In order to test the validity of the relationship between kCN and eqN we *Present address: Departamento de Quimica, Facultad Experimental de Ciencias, Universidad de1 Zulia, M aracaibo, Venezuela. **To whom correspondence should be addressed. 0166-1280/83/$03.00 0 1983 Elsevier Science Publishers B.V.