Intrinsic long range deuterium isotope effects on C-13 NMR chemical shiftsas a conformational probe of benzene derivatives

C-13 NMR spectra of molecules containing one or two benzene rings linked wi th CH=CH2, CH=CH (trans- or cis-), C=C and CH=N groups revealed the existen ce of long range deuterium isotope effects on C-13 chemical shifts. It was found that deuterium isotope effects over six bonds ((6)Delta) are related to the conformation of investigated molecules. Molecular torsional angles w ere calculated by ab initio HF/6-31G* and AM1 semi-empirical calculations. Very good linear correlations were established between experimentally obser ved (6)Delta and theoretical torsional angles obtained from ab initio and s emi-empirical calculations.