Ab initio study of charge transfer between lithium and para-disubstituted benzenes

The present work examines how substituents affect the interaction of lithium with the benzene ring and considers whether two configurations, “loose” and “tight,” can be found for the investigated set of complexes as in the lithium complexes with polyaromatic hydrocarbons. The two conformations were actually found for the electron-donating substituents, whereas for the electron-withdrawing substituents, CF 3 and NO 2 , only tight conformation could be optimized. For complexes in the loose conformation [with the N(CH 3 ) 2 , NH 2 , OH, H, Cl, and CH 3 substituents], the transfer of electron density was directed from the region occupied by a disubstituted benzene to that occupied by Li. The amount of transferred density was very similar for all the complexes (0.21–0.25 a.u.). By contrast, in the tight complexes, the density transfer direction was opposite and the amount of the transferred density depended on the electronegativity of the substituents on benzene ring, being −0.09, −0.09, −0.13, −0.15, −0.15, −0.20, and −0.30 a.u. for N(CH 3 ) 2 , NH 2 , OH, H, Cl, CF 3 , and NO 2 , respectively. Geometries of the loose and tight conformations differed notably. The six-membered ring was significantly more warped in the tight conformation than in the loose one: In the latter, the ring was nearly planar, whereas in the former, the ring had the boat structure.