The Regioselectivity in the Reaction of Monosubstituted p-Benzoquinones with Aromatic Amines

Abstract

The regioselectivity in the reactions of monosubstituted p-benzoquinone (1) (substituent: a: OMe; b: F; c: Cl; d: COMe; e: COPh; f: COOMe; g: CN; h: Ph; i: p -0₂NC₆H₄, j;p-Me₂NC₆H₄) with N, Ndimethylaniline (2a), N, N-diethylaniline (2b), N, N-dimethyl-m-anisidine (2c) and N, N-diethyl-manisidine (2d) in acetic acid was studied by means of two semi-empirical molecular orbital methods (CNDO/2, MNDO). The regioselectivity found in cases of 1h-j could not be accounted by the LUMO coefficients calculated for neutral 1. On the other hand, those for protonated 1 agreed very well with experimental results except for 1c in which regioselectivity was low. Thus, the largest LUMO coefficients were found at C-5 in 1a and 1b, C-3 in 1d-g, and C-6 in 1h-j, respectively, they are in good agreement with the regioselectivities from experiments. In addition, the LUMO energy levels of 1 are lowered when protonated by acetic acid, which would make the interation easier with the HOMO of 2. It seems that those energy level falls in protonated 1 promote the reaction of 1 with 2.