Potential Functions for Internal Rotation about the Csp2-O Bond and Intramolecular Interactions in p-RC6H4OCH3 Compounds

Potential functions for internal rotation about the Csp²ÄO bond in p-RC₆H₄OCH₃ compounds (R = NH₂, OCH₃, CH₃, H, F, Cl, CN, NO₂) were determined by nonempirical quantum-chemical calculations in the HF/6-31G* and MP2/6-31G* approximations with account taken of correlation energy for all electrons. The molecular conformation is planar. The height of the rotation barrier changes, depending on the electronic effect of para-substituent. Electron-donor substituents reduce while electron-acceptor substituents enhance the stability of the planar conformation. Using the natural bond orbital (NBO) approach, the nature of lone electron pairs on the methoxy oxygen atom was analyzed, and the energies for their resonance interaction with the antibonding aromatic * orbitals were determined. The effect of para-substituent on the electron density distribution over the methoxy group and on the Koopmans first ionization potentials was estimated. Geometric parameters of the molecules under study are given.