CRYSTAL AND MOLECULAR-STRUCTURE OF 1,3-(DIS TAL) DERIVATIVES OF P-TERT-BUTYL CALIX[4]ARENE - EVIDENCE FOR CONFORMATIONAL CONTROL AND SELF-INCLUSION INVOLVING WEAK C-H...PI INTERACTIONS/

X-Ray crystallographic analyses of four p-tert-butylcalix[4]arenes in which two 1,3-(distal)phenolic groups on the lower rim have been deriv atised with cyanomethyl, amino ester and alkyl acetate residues, are r eported. Intramolecular hydrogen bonding between the free phenolic gro ups and their proximal ethereal oxygen atoms is evident in all four co mpounds. With the exception of the ethyl ester, these calixarenes adop t very distorted cone conformations in the solid state. The ethyl este r adopts a much less distorted cone conformation with the distinguishi ng feature of self-inclusion of an ethoxy residue of one ester group o n the lower rim within the hydrophobic cavity of a neighbouring molecu le within the crystal. Factors which control the conformations of thes e molecules are discussed.