Comparison of the lengths of molecules in urea and in thiourea adducts

Abstract

For some compounds it is possible to form both a urea and a thiourea adduct (inclusion compound). When the length of channel occupied by a molecule of the compounds is measured with the use of continuous layer lines in the x-ray diffraction pattern of a single crystal of the adduct, the length measured in thiourea is appreciably shorter than that measured in urea. The channel length occupied by a molecule depends mainly upon 1. the number of atoms in the chain, 2. the degree of coiling, 3. the amount of overlapping of the ends and, 4. whether the guest is “locked into” the structural features of the host.