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Configurations and conformations in acyclic, unsaturated hydrocarbons. A 13 C NMR study
Author(s) -
de Haan J. W.,
Van de Ven L. J. M.
Publication year - 1973
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270050309
Subject(s) - geminal , chemistry , allylic rearrangement , nerol , steric effects , cis–trans isomerism , nmr spectra database , stereochemistry , geraniol , crystallography , spectral line , computational chemistry , organic chemistry , physics , chromatography , astronomy , essential oil , catalysis
Abstract 13 C NMR (CMR) spectra of a number of di‐ and trisubstituted ethylenes have been measured. Very consistent values are found for the differential shieldings of allylic carbons in a number of linear, (Z)‐ and (E)‐disubstituted ethylenes. The discrepancies between the several structural elements are explained tentatively by assuming different rotational preferences in the (Z)‐isomers, the (E)‐isomers, or both. The results obtained for some branched olefins are qualitatively in agreement with conclusions reached in previous 1 H NMR (PMR) investigations, with the possible exception of 2,5‐diMe‐3‐hexene. Differential shieldings in trisubstituted ethylenes are larger than in disubstituted ethylenes, probably as a consequence of steric interaction between geminal substituents. It is confirmed, that API's recent relabelling of the isomers of 3‐Me‐2‐hexene was justified. Furthermore, the (E)‐configuration is assigned to the high‐boiling isomer of 3,4,4‐triMe‐2‐pentene. On the other hand, the high‐boiling isomer of 3‐Et‐4‐Me‐2‐pentene is shown to be the (Z)‐isomer. For the isomeric pair of geraniol and nerol, the (E)‐configuration is assigned to the former and the (Z)‐configuration to the latter, in agreement with our recent PMR investigations.