Structural dependence of isotope effects in H and C nuclear magnetic resonance spectra of the trans-N-benzylideneaniline imino group

Deuteriumand N-induced isotope effects on H and C chemical shifts of the imino moiety of 16 trans-N-benzylideneaniline (tBA) isotopomers were determined and analysed. These effects appear to be a sensitive probe of molecular conformation and its changes. All determined deuterium isotope effects on the imino-proton are small and negative and are spread in the range from −0.88 ppb in 4-H-tBA to −4.97 ppb in H10-tBA. The effects on the imino-carbon are either positive or negative and have much larger values. Negative sign of isotope effects is primarily governed by lone-pairs, while magnitude and non-additivity depend on the site of isotopic substitution, molecular conformation and distribution of rotamer populations. All N isotope effects on both H and C chemical shifts are positive. A comparison of isotope effects in tBA with those in related isoelectronic compounds is made. © 1998 Elsevier Science B.V. All rights reserved.