title: Conformation of some biologically active aromatic ureas.
abstract: Experimental IR spectroscopic data for the N-H stretching mode frequencies for several types of tri-substituted ureas containing benzyl and/or phenyl substituents as well as theoretical results from B3LYP/6-31G(d,p) computations on selected compounds provide sufficient evidence to determine the conformational state of these molecules. Two types of N-H bands may be found the spectra: (a) A type band due to a classical trans conformation (trans I) of the CONH structure; (b) B type band arising from an alternative trans form (trans II), in which the N-H band is involved in a hydrogen bond like interaction with the aromatic ring at the neighbouring nitrogen atom (benzyl or phenyl substituents). The N-H band of trans ICONH structure is observed at frequencies higher than 3460 cm-1, the actual position depending on weather the non-substituted N-H group is linked to aryl or alkyl substituents. The N-H band of the trans II rotameric structure is observed at 3430-3420 cm-1.
authors.affiliation: Department of Chemistry, University of Sofia, 1 James Bourchier Avenue, 1164 Sofia, Bulgaria.
authors.forename: Boriana
authors.initials: B
authors.lastname: Hadjieva
authors.forename: Sonia
authors.initials: S
authors.lastname: Ilieva
authors.forename: Diana
authors.initials: D
authors.lastname: Cheshmedzhieva
authors.forename: Boris
authors.initials: B
authors.lastname: Galabov
mesh_terms: D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008962:Models, Theoretical; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D014508:Urea / Q000737:chemistry*
chemical_list: D006859:Hydrogen; D014508:Urea; D009584:Nitrogen