A doubly hermaphroditic chiral crown ether

A single-crystal structure determination on the S-protected form of a chiral 18-crown-6 derivative known to be a selective catalyst for thiolysis reactions of amino acid derivatives has shown the molecule to crystallise in an unsolvated form where the macrocyclic ring has a conformation in which the dipoles of substituent amide units are aligned parallel. The resulting polar entities are linked through NH center dot center dot center dot O H-bonds and weaker interactions which can be considered to result in doubly hermaphroditic links, the whole crystal proving to be polar. The possible consequences of the observed secondary interactions, some being intramolecular, are considered in relation to the mechanism of catalysis by the isolated molecule.