Structural dependence of isotope effects in 1H and 13C nuclear magnetic resonance spectra of the trans-N-benzylideneaniline imino group
摘要:
Deuterium-and N-15-induced isotope effects on H-1 and C-13 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-2-tBA to -4.97 ppb in H-2(10)-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-15 isotope effects on both H-1 and C-13 chemical shifts are positive. A comparison of isotope effects in tBA with those in related isoelectronic compounds is made. (C) 1998 Elsevier Science B.V. All rights reserved.