On the unusual 2JC2-Hf coupling dependence on syn/anti CHO conformation in 5-X-furan-2-carboxaldehydes

Carlos Pérez*, Reynier Suardíaz, Pedro J. Ortiz, Rachel Crespo-Otero, Gloria M. Bonetto, José A. Gavín, José M. De La Vega García, Jesus San Fabián, Rubén H. Contreras

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

A remarkable difference for 2JC2-H f, coupling constant in syn and anti conformers of 5-X-furan-2-carboxaldehydes (X = CH3, Ph, NO2, Br) and a rationalization of this difference are reported. On the basis of the current knowledge of the Fermi-contact term transmission, a rather unusual dual-coupling pathway in the syn conformer is presented. The additional coupling pathway resembles somewhat that of the JH-H in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the πC=C electronic system. The homoallylic coupling pathway can be labeled as σ*C-H ←-πc=c → σ*C-H. In the present case, this additional coupling pathway, using an analogous notation, can be labeled as σ* c2-cc ← LP1(O 1)⋯ LP2(Oc) → σ* Cc-Hf (σ*C2 -C c) where O1 and Oc stand for the ring and carbonyl O atoms, respectively. This additional coupling pathway is not activated in the anti conformers since both oxygen lone pairs do not overlap.

Original languageEnglish
Pages (from-to)846-850
Number of pages5
JournalMagnetic Resonance in Chemistry
Volume46
Issue number9
DOIs
Publication statusPublished - 1 Sep 2008

Keywords

  • Fermi-contact transmission
  • Furfural
  • Geminal NMR couplings
  • NBO
  • Through space

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