Organic anions. Part 5. On the nature of the prop-2-ynyl/allenyl anion

Abstract

Ab initio MO calculations on the prop-2-ynyl/allenyl anion (1) suggest that it adopts an ‘allene-like’ geometry (4) and it seems likely that this is associated with a concentration of charge at the less substituted (CH) end of the molecule. On the other hand both CNDO II MO calculations and spectroscopic studies on the 1,3-diphenyl substituted anion (9) suggest that it adopts a ‘planar’ geometry (Figure 2) with the charge concentrated at the more substituted (CHPh) end of the molecule. This dependence of geometry and charge distribution on the degree of conjugation allows a number of earlier, apparently contradictory observations, to be rationalised.