ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The ‘Push-Poll’ Effect of ‘Push-Pull’ Oligoacetylenes. A 13C-NMR InvestigationAccording to 13C-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 13C labelling of the CO group of 3a.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19910740713
