ACIDITY OF DIBASIC CARBON ACIDS .2. GEOMETRY AND ELECTRONIC-STRUCTUREOF MONO-ANIONS AND DI-ANIONS OF 9,10-DIHYDROANTHRACENE AND ITS DERIVATIVES IN TETRAHYDROFURAN
M. Nir et al., ACIDITY OF DIBASIC CARBON ACIDS .2. GEOMETRY AND ELECTRONIC-STRUCTUREOF MONO-ANIONS AND DI-ANIONS OF 9,10-DIHYDROANTHRACENE AND ITS DERIVATIVES IN TETRAHYDROFURAN, Perkin transactions. 2, (7), 1995, pp. 1433-1442
The geometric structure, charge distribution and heats of formation of
9-R(1)-10-R(2)-9,1 0-dihydroanthracenes (R(1) = R(2) = H; R(1) = Me,
R(2) = H; R(1) = R(2) = Me; R(1) = Ph, R(2) = H; R(1) = R(2) = Ph; R(1
) = CN, R(2) = H), their mono- and di-anions; deprotonated at position
s 9 and 10 have been calculated by the AM-1 method. The C-13 chemical
shifts of the mono- and di-alkali metal salts have been determined in
[H-2(8)]THF. The structures of the mono- and di-anions are nearly plan
ar, the dianions being more planar than the monoanions. The hybridizat
ion of the deprotonated carbon atoms is nearly sp(2). Phenyl substitue
nts subtend angles of 56.5 degrees and 45.0 degrees to the anthracene
plane in the mono- and di-anions, respectively. With the exception of
the cyano group, there is little participation by the substituents in
the delocalization of negative charge. There is a correlation between
the pi-electron densities and the change in C-13 chemical shift upon a
nion formation from the neutral species. The values of the proportiona
lity constants are equal to 120.3 and 133.1 ppm/electron for mono- and
di-anions, respectively. The pattern of negative charge distribution
in the monoanions of 9,10-dihydroanthracenes is similar to that of sub
stituted diphenylmethanes. The first and second acidity constants of s
ubstituted 9,10-dihydroanthracenes in the liquid phase follow the patt
erns indicated by the gas phase calculations of their relative thermod
ynamic stabilities.