An ab initio study of the p,π interaction: III. Interaction of an ether oxygen atom with a double bond

RHF/6-311G(d) calculations were performed for the H₂C=CHOCH₃ and H₂C=CClOCH₃ molecules with full geometry optimization and at varied angles of rotation of the methoxy group about the C-O bond, with all the other geometric parameters optimized. The first molecule has one energy minimum and one transition state, and the second molecule, two minima. Changes in the populations of the p _y orbitals of the olefinic carbon and oxygen atoms (orbitals whose symmetry axes are perpendicular to the molecular plane) and in the fractional charges on these carbon atoms, occurring upon rotation of the methoxy groups about the C-O bonds, cannot be attributed to changes in the extent of the p,π conjugation between the lone electron pairs of the oxygen atoms and π electrons of the C=C bonds.