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Der ‘Push‐Pull’‐Effekt von ‘Push‐Pull’‐Oligoacetylenen. Eine 13 C‐NMR‐Untersuchung
Author(s) -
Neuenschwander Markus,
Bartlome Andreas
Publication year - 1991
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19910740713
Subject(s) - push pull , chemistry , acetylene , delocalized electron , stereochemistry , push and pull , crystallography , organic chemistry , mechanical engineering , electrical engineering , engineering
The ‘Push‐Poll’ Effect of ‘Push‐Pull’ Oligoacetylenes. A 13 C‐NMR Investigation According to 13 C‐chemicaI shifts of ‘push‐pull’ oligoacetylenes 1 – 4 , the ‘push‐pull’ effect ( i.e. π delocalization induced by ‘push‐pull’ substituents) rapidly decays in this series. To correct for other than π ‐charge‐density effects, Δδ values of symmetrically placed C‐atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C‐atoms of PP‐ketones 1a – 3a and PP ‐esters 1b – 4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push‐pull’ triacetylenes 3 have been solved by 13 C labelling of the CO group of 3a .