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On the unusual 2 J C 2 H f coupling dependence on syn / anti CHO conformation in 5‐X‐furan‐2‐carboxaldehydes
Author(s) -
Pérez Carlos,
Suardíaz Reynier,
Ortiz Pedro J.,
CrespoOtero Rachel,
Bonetto Gloria M.,
Gavín José A.,
García de la Vega José M.,
Fabián Jesús San,
Contreras Rubén H.
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2268
Subject(s) - chemistry , conformational isomerism , lone pair , stereochemistry , crystallography , pi , coupling (piping) , sigma , furan , molecule , physics , mechanical engineering , biochemistry , organic chemistry , quantum mechanics , engineering
A remarkable difference for 2 J C 2 H fcoupling constant in syn and anti conformers of 5‐X‐furan‐2‐carboxaldehydes (X = CH 3 , Ph, NO 2 , 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 J HH in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the π CC electronic system. The homoallylic coupling pathway can be labeled as σ* CH ← π CC → σ* CH . In the present case, this additional coupling pathway, using an analogous notation, can be labeled as σ* C 2 C C← LP 1 (O 1 )··· LP 2 (O C ) →σ* C C H f(σ* C 2 C C) where O 1 and O C 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. Copyright © 2008 John Wiley & Sons, Ltd.