Methylene chloride-soluble and insoluble ureines An X-ray diffraction, infrared absorption, and proton magnetic resonance study

An X-ray diffraction study has been carried out on single crystals of two symmetrical ureines (N,N′-diiopropylurea and the familiar N,N′-dicyclohexylurea) and one unsymmetrical ureine (N-tert.-butyl.N′-methylurea). The presence/absence of intermolecular H-bonds in the crystal state has been compared to the situation assessed in solution by 1H n.m.r. It was shown by i.r. absorption that soluble ureines may disrupt intermolecular (peptide)N—H- O=C(peptide) H-bonds in methylene chloride, a point of practical interest, particularly in solid-phase peptide synthesis.