Natural J coupling (NJC) analysis of the electron lone pair effect on NMR couplings: Part 1. the lone pair orientation effect of an α-nitrogen atom on1J(C,C) couplings

Verónica Barone, Juan E. Peralta, Rubén H. Contreras, Anton V. Sosnin, Leonid B. Krivdin

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Abstract

The known lone pair orientation effect of an α-nitrogen atom on 1J(C,C) couplings was studied using the natural J coupling (NJC) dissection method for the Fermi contact (FC) term. This dissection was performed at the DFT-B3LYP level using three different basis sets. It was verified that non-contact contributions, which are much smaller than the FC term, do not depend on the orientation of the N lone pair. Acetone oxime (1), protonated acetone oxime (2) and ethylamine (3), were taken as model compounds to perform this study. In 1 the difference between 1J(Z) and 1J(E) is mainly determined by three NJC terms, i.e the nitrogen lone pair, the carbon-carbon bond containing the coupled carbon atoms and the carbon inner core orbitals contributions. In 3 the angular dependence of 1J(C,C) vs the amine group conformation is dominated by the same three contributions that define the 1J(Z) and 1J(E) difference in 1.

Original languageEnglish
Pages (from-to)600-606
Number of pages7
JournalMagnetic Resonance in Chemistry
Volume39
Issue number10
DOIs
StatePublished - 2001

Keywords

  • Bond contributions
  • Indirect spin-spin couplings
  • Lone-pair effect
  • NMR
  • Natural j couplings
  • Nbo interactions

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