Ii. Bilkis et al., REDUCTIVE ALKYLATION OF ARENES .5. ANIONIC PRODUCTS OF THE 2-ELECTRONREDUCTION OF AROMATIC NITRILES IN LIQUID-AMMONIA, Journal of physical organic chemistry, 7(3), 1994, pp. 153-161
The reduction of 9-cyanoanthracene by two equivalents of potassium in
liquid ammonis was shown to yield the 9-cyanoanthracene dianion, where
as 1-naphtho- and benzonitrile gave the cyanodihydroaryl anions corres
ponding to the protonation of nitrile dianions at a position para to t
he cyano group. The 9-cyanoanthracene dianion underwent the same trans
formation in the presence of a stronger protonating agent, methasol. A
ccording to C-13 NMR spectral data of the generated specks, the cyano
group extracts the negative charge from the pi-electronic system: ca 0
.20:0.25 e in the case of the 9-cyanoanthracene dianion and ca 0.14:0.
17 e in the case of cyanodihydroaryl anions. These estimations and the
general NMR pattern of pi-charge distribution in all the anionic spec
ies under investigation are in accordance with data from quantum molec
ular orbital calculations at the PM3 and INDO levels, being reflected
by the fairly good linear relationships between the changes of ring ca
rbon chemical shifts on going to the anionic species from the respecti
ve neutral precursors on the one hand and the calculated pi-charges on
the other. The para-orienting effect of the cyano group in the proton
ation of nitrile dianions is discussed in terms of the pi-charge distr
ibution in the starting dianion and the tendency to form a most stable
cyanodihydroaryl anion isomer.