title: Association of N-(pyridin-2-yl),N'-substituted ureas with 2-amino-1,8-naphthyridines and benzoates: NMR and quantum chemical studies of the substituent effect on complexation.
abstract: Association of four N-(pyridin-2-yl),N'-R(1)-ureas (R(1) = ethyl, n-butyl, phenyl, and tert-butyl) with substituted 2-amino-1,8-naphthyridines and benzoates were studied by (1)H NMR spectroscopic titrations and quantum chemical calculations. The benzoates and 2-amino-1,8-naphthyridines were selected as representatives of double and triple hydrogen bonding counterparts, respectively. The classical substituent effect on the association was studied. A prerequisite and a crucial step for the complex formation was the breaking of the intramolecular hydrogen bond in urea derivatives. The QTAIM calculation method was employed to explain the hydrogen bonding within complexes. In the case of benzoates carrying an electron-donating substituent the experimental findings were explained by the formation of two complexes. These observations were rationalized by the electronic repulsions between atoms in a close proximity and further verified by calculations. Single-crystal X-ray diffraction was used to confirm the structure of studied ureas in the crystalline state. These results are in line with the solution studies of self-association of ureas.
authors.affiliation: Faculty of Chemical Technology and Engineering, University of Technology and Life Sciences, Seminaryjna 3, PL-85-326 Bydgoszcz, Poland. borys.osmialowski@utp.edu.pl
authors.forename: Borys
authors.initials: B
authors.lastname: Ośmiałowski
authors.forename: Karina
authors.initials: K
authors.lastname: Mroczyńska
authors.forename: Erkki
authors.initials: E
authors.lastname: Kolehmainen
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kowalska
authors.forename: Arto
authors.initials: A
authors.lastname: Valkonen
authors.forename: Marek
authors.initials: M
authors.lastname: Pietrzak
authors.forename: Kari
authors.initials: K
authors.lastname: Rissanen
mesh_terms: D001565:Benzoates / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009287:Naphthyridines / Q000737:chemistry*; D011789:Quantum Theory; D014508:Urea / Q000031:analogs & derivatives / Q000737:chemistry*
chemical_list: C427025:2-amino-1,8-naphthyridine; D001565:Benzoates; D009287:Naphthyridines; D014508:Urea