Intramolecular Interactions of Phosphor-Containing Groups with an Aromatic Fragment in Different Conformations

Abstract

Abstract Geometrical and electronic structure of conformers was studied by optical spectroscopy and quantum chemistry methods. The interaction mechanism of phosphor-containing groups with an aromatic fragment in YC6H4PX2 (Y = H, Cl, Me, OMe, NMe2, C(O)OR; × = Alk, OAlk, NAlk2, Cl) and YC6H4P(Z)X2 (Y = H, C1, Me, OMe, NMe2; × = Alk, OAlk, NAlk2, F, C1; Z = O, S) compounds is discussed. In case of bisector conformation (A), where the benzene ring plane coincides with a XPX-angle bisectrix, ll-acceptor action of phosphorus-containing groups increases with X varying in a series: Alk <NAlk2 ≈ OAlk ≤ F4 << C1. These properties are displayed in ground and excited states of molecules, and are determined by interaction of PX2 and P(Z)X2 vacant group orbitals antisymmetric with respect to bisector plane with aromatic fragment π-orbitals. For phosphorchloride groups [sgrave]-π-conjugation dominates and the d-π-conjugation contribution is small. π-acceptor effect for P(0)X2is weaker than for PX2 and P(S)X2 groups (especially in excited states) which is due to competitive transfer of electron density from oxygen to PX2 fragment. In case of the gonal conformation (B) where benzene ring and bisector plane of PX2 fragment are perpendicular, π-donor effect of PAlk2 group is found to be 2–4 times weaker than for NAlk2. According to quantum-chemical calculations with the MNDO method ArPX2 the stabilization of conformer B for ArPX2 increases in a series X: C1 <C=N <F <H <CH3; and for ArP(0)X2 the main conformation is (A).