| Sumario: | Interactions which define the planar conformation of the methoxy group with respect to the aryl ring in methyl aryl ethers are studied by 13C NMR spectroscopy and by MO calculations at the AM1 level in a family of anisole derivatives with unhindered ortho positions. Different methoxy ortho substituent chemical shifts were found and they were ascribed to different populations of the two coplanar conformers of the methoxy group. Optimized geometries, total energies, total point-charge dipole moments and II bond orders of the aromatic CC bonds for both methoxy rotamers of each of these compounds were calculated. Results suggest that the different populations of both types of rotamer arise from an electrostatic interaction between the side-chain dipole moment and an opposite dipole moment induced on the II electronic system of the aromatic CipsoCortho bond oriented s-cis to the methyl moiety of the methoxy group. The strength of this interaction depends on the II bond order of that bond. The failure of the AM1 method to describe quantitatively the energy of this interaction is discussed. © 1995.
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