Hydrogen-bonded complexes of nicotine with simple alcohols

Ab initio and density functional theory studies have been performed on the hydrogen-bonded complexes of neutral and protonated nicotine with ethanol, methanol, and trifluromethanol to explore their relative stability in a systematic way. Among all the hydrogen-bonded nicotine complexes considered here, protonated forms in nicotineethanol and nicotinemethanol, and neutral form in nicotinetrifluromethanol complexes have been found to be the most stable. In the former two complexes, the proton attached to the pyrrolidine nitrogen acts as a strong hydrogen bond donor, whereas the pyrrolidine nitrogen atom acts as a hydrogen bond acceptor in the latter case. Neutral complex of nicotine with trifluromethanol has been found to possess a very short hydrogen bond (1.57 angstrom) and basis set superposition error corrected hydrogen bond energy value of 19 kcal/mol. The nature of the various hydrogen bonds formed has been investigated through topological aspects using Bader's atoms in molecules theory. From the calculated topological results, excellent linear correlation is shown to exist among the hydrogen bond length, electron density, and its Laplacian at the bond critical points for all the complexes considered. The natural bond orbital analysis has been carried out to investigate the charge transfer in the nicotine alcohol complexes. In contrast to the blue shifting behavior that is generally exhibited by other C-H...O hydrogen bonds involving sp3 carbon atom, the C-H...O hydrogen bond in the protonated nicotineethanol and methanol complexes has been found to be proper with red shifting in nature. (c) 2011 Wiley Periodicals, Inc.