Intramolecular hydrogen bond strength of 3-methyl-4-amino-3-penten-2-one, an experimental approach

The intramolecular hydrogen bonding of 3-methyl-4-amino-3-penten-2-one, 3-MeAPO, has been investigated by experimental results, including NMR, IR, and UV spectra. According to 1H-NMR spectrum, the titled molecule is as a keto-amine form. The vibrational spectra of 3-MeAPO and its deuterated analogous have been recorded. The existence of intermolecular and intramolecular hydrogen bond is also shown in both solid and solution phases. The DFT suggested a relatively medium intramolecular hydrogen bond with N···O distance at 2.597 Ǻ for 3-MeAPO, which is in agreement with the calculated hydrogen bond energy about 10.85 kcal/mol for the mentioned molecule. In the IR spectrum of 3-MeAPO, the mode sNH(NHin) observed at 3135 cm-1 in the CCl4 solution, and NH at 10.32 ppm. The mentioned bands are in 3184 cm-1 [1] and 9.7 ppm [2] for 4-amino-3-penten-2-one (APO), See fig.1. The UV-Vis spectrum of 3-MeAPO was recorded in ethanol, as solvent. The UV-Vis spectra of 3-MeAPO and APO are shown a band at 319 and 299 nm [3], respectively. The theoretical calculations and spectroscopic results indicate that the intramolecular hydrogen bonding (IHB) strengthof 3-MeAPO is stronger than that in 4-amino-3-penten-2-one (APO).