DFT studies of the structure, vibrational and NMR spectra of 2-amino-pyridine betaine monohydrate

✍ Scribed by M. Szafran; I. Kowalczyk; J. Koput

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 284 KB
• Volume: 754
• Category: Article
• ISSN: 0022-2860
• DOI: 10.1016/j.molstruc.2005.06.029

✦ Synopsis

Four of the most stable conformers of 2-amino-pyridine betaine (1-carboxymethyl-2-amino-pyridinium inner salt) monohydrates, 2-NH 2 PB$H 2 O, and one anhydrous were analyzed by the B3LYP/6-31G(d,p) calculations and compared with the X-ray data. Two types of optimized conformers can be distinguished: (a) with NH 2 and COO groups and (b) an imino tautomer with NH and COOH groups. A common feature of the optimized molecules are intramolecular hydrogen bonds between the COO K and H 2 N or COOH and HN groups. In the crystal both NH 2 and COO groups participate in intermolecular hydrogen bonds. The probable assignments of the anharmonic experimental solid state vibrational frequencies of 2-NH 2 PB$H 2 O and 2-ND 2 PB$D 2 O (conformer 2) based on the calculated B3LYP/6-31G(d,p) harmonic frequencies have been made. Correlations between experimental chemical shifts for 2-NH 2 PB, its hydrochloride and 1carboxyethyl-2-amino-pyridinium inner salt ( 13 C and 1 H in D 2 O) and GIAO/B3LYP/6-31G(d,p) calculated isotropic shielding constants, d exp ZaCbs calc , are reported. Good linear regression between experimental and theoretical results for 13 C was obtained. Only in 2-NH 2 PB the hydrogen at a-position is outside the linear correlation.