Nuclear magnetic resonance studies of 1,3-butadienes

Author: Cunliffe A.V.   Harris R.K.  

Publisher: Taylor & Francis Ltd

ISSN: 1362-3028

Source: Molecular Physics, Vol.13, Iss.3, 1967-01, pp. : 269-282

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

The treatment of Karplus for the pi-electron contribution to proton-proton coupling constants is extended in this paper to conjugated systems. The equation derived is applied to s-trans and s-cis 1,3-butadienes, and the coupling constants obtained are compared with the experimental values. It is concluded that the five bond coupling constants 5 J tc and 5 J cc (the subscripts c and t refer to the cis or trans orientation of the bonds of the coupling path—see Part I) in the s-trans molecule are due to a pi mechanism, and that for cyclohexadiene the five bond coupling constant has a large contribution from this effect. The results for the four bond couplings are less conclusive, but it is suggested that a pi mechanism is dominant in s-trans dienes, whereas a sigma mechanism dominates for cyclohexadiene.