ELECTROSTATIC EFFECT OF THE POLAR BOND POLARIZABLE BOND INTERACTION ON C-13 CHEMICAL-SHIFTS

In the present work, a theoretical analysis was carried out on the eff ect of the proximity of a polar bond to a polarizable bond on the magn etic shielding constants of the nuclei belonging to the polarizable bo nd. In particular, the case of C-13 magnetic shielding constants in a vinylic C=C bond is considered. The electric field of the polar bond i s simulated by two opposite point charges proximate to the C=C bond in (I) C2H2 and (II) (OH)HC2H2. Changes in the C-13 magnetic shieldings as well as the polarization of the a C=C bond are evaluated as a funct ion of the magnitudes of such point charges. The shielding effect on t he C nucleus proximate to the positive charge is of the same order of magnitude as that experimentally determined in aryl methyl ethers. The present analysis yields theoretical support to the assumption that ch anges in magnetic shielding constants can be adequate probes to detect the stabilization effect in a molecular system originating in an elec trostatic interaction between a polar bond proximate to a polarizable bond. (C) 1998 John Wiley & Sons, inc.