engleski

Isotope Effects on Chemical Shifts in Benzene Derivatives

Isotope effects on NMR parameters: chemical shifts, coupling constants and relaxation times, give valuable information on molecular structure and dynamics in solution. Long range effects, i.e. those transmitted over more than three bonds from the site of the isotopic substitution, reflect averall molecular geometry and can be used in conformational studies. Deuterium-induced isotope effects in H-1 NMR spectra have rarely been observed owing to a narrow H-1 chemical shift range. We have, therefore, prepared a series of deuteriated benzene derivatives of the Ph-Z-Ph type, where Ph refers to the phenyl, while Z is the bridging group, and recorded and analysed their H-1 NMR spectra with 300 and 360 MHz NMR spectrometers. The sign, magnitude and slight nonadditivity of isotope effects on H-1 chemical shifts depend on the site of the isotopic substitution, steric and lone-pair interactions, conformation and distribution of rotamer populations.

nije evidentirano

nije evidentirano