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Structural dependence of isotope effects in H-1 and C-13 NMR spectra of the trans-N-benzylideneaniline imino group

Deuterium- and 15N-induced isotope effects on 1H and 13C 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 4-2H-tBA to − 4.97 ppb in 2H10-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 15N isotope effects on both 1H and 13C chemical shifts are positive. A comparison of isotope effects in tBA with those in related isoelectronic compounds is made.

NMR ; isotope effects ; conformation ; trans-n-benzylideneaniline

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