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.
Synthesis and x-ray molecular structure of monodeoxycalix[5]arenes
A monodeoxycalix[5]arene was synthesized by stepwise methods. The structure found in crystal by X-ray diffraction is a 'partial cone' in which four contiguous phenol units form a helical intramolecular hydrogen bonding array and the OH-depleted ring has an inverted arrangement. N. O. E experiments support the partial cone structure in solution.