Structural characterization of β-2′ pyridylaminocrotonoyl-2-pridylamide by ESI-MS, NMR, single crystal X-ray analysis and ab initio methods

In contradiction with earlier reports H-1, C-13 and N-15 NMR spectra show that beta-2'-pyridylaminocrotonoyl-2-pyridylamide is the only form present in chloroform solution. According to the X-ray data the same tautomer exists also in the crystal state. The studied amide has a dimeric form where the monomer molecules are held together by two intermolecular hydrogen bonds. The NMR spectral data show that there is also an intramolecular hydrogen bond in each monomer subunit. The dilution experiments and variable-temperature H-1 NMR runs show that beta-2'-pyridylaminocrotonoyl-2-pyridylamide tends to form the dimers also in chloroform solution at higher concentrations. The ESI-TOF MS measurements at different concentrations confirm that there is a dimerization process taking place in solution. The calculated energetic effect of dimerization of beta-2'-pyridylaminocrotonoyl-2-pyridylamide in vacuum is equal to -34 kJ/mol (exothermic process). X-ray analysis shows that the molecule in crystalline state is not planar. The ab initio RHF/6-31 G** calculations approximate well the X-ray determined molecular geometry of beta-2'pyridylaminocrotonoyl-2-pyridyl-amide. (C) 2003 Elsevier Science B.V. All rights reserved.