Conformational isomers of the trimethyl ethers of monodeoxycalix[4]arenes

The conformational analysis of title compounds using X-ray crystallographic analysis and molecular mechanics calculations is presented. The (u,u,d) conformer is the most stable among three possible forms. Solvent polarity plays a significant role in its conformational dynamic equilibrium. In the most stable form, the orientation of the methoxyl group of the inverted anisole ring is inside a cavity created by the remaining three aromatic rings as was found in the structure of one of the derivatives in its crystalline state. This cavity filling inward orientation of the alkoxyl group is quite a characteristic feature for the trimethyl ethers of the monodeoxycalix[4]arenes.