Critical assessment of the intramolecular hydrogen bonding (IMHB) interaction in two isomeric hydroxynicotinic acids: A computational approach Aniruddha Ganguly, Soumen Ghosh, Nikhil Guchhait ⇑ Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Calcutta 700009, India article info Article history: Received 25 April 2014 Received in revised form 6 June 2014 Accepted 30 June 2014 Available online 8 July 2014 Keywords: Density functional theory Intramolecular hydrogen bonding Atoms-In-Molecule Bond critical point Natural Bond Orbital Resonance assisted hydrogen bond abstract Density Functional Theory (DFT) based computational study has been performed to characterize intramo- lecular hydrogen bonding (IMHB) interaction in two isomeric hydroxynicotinic acids viz. 3-hydroxyison- icotinic acid (3HINA) and 4-hydroxynicotinic acid (4HNA). The IMHB interaction has been analyzed by the calculation of electron density q(r) and Laplacian r 2 q(r) at the bond critical point using Atoms-In- Molecule (AIM) theory. Topological features and energy densities based on q(r) through the perturbation of the IMHB distances suggest that at equilibrium geometry the IMHB interaction develops certain char- acteristics typical of a covalent interaction. Concomitantly, the role of charge transfer interaction in the IMHB has been critically addressed under the provision of Natural Bond Orbital (NBO) analysis. The assis- tance of resonance in the IMHB interaction present in these molecular systems is also delineated from quantum chemical calculations. The comparatively greater IMHB energy for 4HNA with respect to its iso- mer has also been attempted to address critically along with the argument about the superiority of quan- tum chemical criteria over geometrical criteria for the assessment of IMHB interaction in the studied compounds. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Despite being characterized as a weak interaction, Hydrogen bonding (HB) has always been a key element to a plethora of activ- ities in nature. By virtue of its unique properties like directionality, specificity and transience, this non-covalent interaction plays pivotal roles in providing specific shapes to biomolecules and maintaining their functionality which in turn advocates for its inevitability in sustaining life-cycle on this planet [1,2]. Hydrogen bonding (HB) also plays a crucial role in defining the crystal pack- ing of molecules and is the source of specific properties of associ- ated liquids like water and thus crops up as a demanding topic of research [1–3]. A classical hydrogen bond is formed by two heteroatoms, X and Y (having already saturated valencies), with a hydrogen atom bonded to one of them and located approximately in between (XAHY). Mostly, H-bonding has been considered as an electro- static attraction between the positive end of the bond dipole of XAH and the center of negative charge on Y (generally a lone pair of electrons) [4]. Unlike typical chemical bonds, the H-bond ranges over a large scale of energy, from very weak ones to very strong ones depending upon the nature of the groups involved [5]. A par- ticular type of H-bonding interaction is the one often found in association with excited state intramolecular proton transfer (ESIPT) reaction, i.e., the intramolecular hydrogen bond (IMHB) which is a particular case of the interaction occurring within the same molecular architecture. The IMHB interaction is well-docu- mented to have its crucial impact on the feasibility and rate of ESIPT process [6]. Vitamin B 3 or Nicotinic acid is an essential human nutrient known for its involvement in repairing damaged DNA, producing steroid hor- mones in adrenal gland, lowering of plasma lipids and so on and so forth [7]. Nicotinic acid and its derivatives (especially hydroxy deriv- atives) are not only biologically and pharmaceutically important, but are also frequently used in crystallographic studies involving metal organic frameworks (MOFs) and in the synthesis of microporous coordination polymers [8,9]. So, a meticulous understanding of the structure and the H-bonding property of such systems is a must from scientific perspective. Following the aforesaid points, in the present contribution, we have focused on a thorough exploration of IMHB interaction in two isomeric hydroxynicotinic acids viz., 3-hydroxyi- sonicotinic acid (3HINA) and 4-hydroxynicotinic acid (4HNA) from http://dx.doi.org/10.1016/j.comptc.2014.06.027 2210-271X/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 3323508386; fax: +91 3323519755. E-mail address: nguchhait@yahoo.com (N. Guchhait). Computational and Theoretical Chemistry 1045 (2014) 41–46 Contents lists available at ScienceDirect Computational and Theoretical Chemistry journal homepage: www.elsevier.com/locate/comptc