Arguing on the roles of various non-covalent interactions in governing the global stabilization/destabilization of 3-hydroxy-2-pyridin-2-yl- propenal: An AIM-based approach Aniruddha Ganguly ⇑ , Bijan K. Paul, Nikhil Guchhait ⇑ Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Calcutta 700009, India article info Article history: Received 31 May 2017 Received in revised form 20 July 2017 Accepted 3 August 2017 Available online 4 August 2017 Keywords: Atoms in molecules Hydrogen bond Non-covalent interaction Aromatic Stabilization Nucleus Independent Chemical Shift abstract A computational analysis based on the ‘‘Atoms in Molecules” i.e. AIM formalism; of the molecular forces present within 3-Hydroxy-2-pyridin-2-yl-propenal (HPYP) has been undertaken in this contribution. The study presents a critical argument on the regulatory role(s) of hydrogen bonds (HBs) and other non- covalent interactions, viz. HH and NO/OO; toward the structural features as well as global stabiliza- tion and/or destabilization of the aforesaid molecular system. Furthermore, to acquire a comprehensive account of the aromatic stabilization of the framework in the presence of the concerned non-covalent interactions; Nucleus Independent Chemical Shift (NICS) descriptor has been employed. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction The lack of an unequivocal definition of the ‘‘chemical bond” has led to the continuous controversy of whether or not a particu- lar pair of atoms can be considered as bonded [1]. However, the quantum mechanical description proposed by Bader (known as the Atoms in molecules i.e. AIM formalism), which mainly relies on the topology of the electron density q(r), a physically observ- able quantity; provides a unique definition of the bonding phe- nomenon by virtue of the concept of ‘‘band path” (BP); a line following the ridge of maximum charge density between a pair of nuclei [1–5]. Besides the conventional Lewis structures, Bader’s theory also faithfully reproduces a plethora of weak interactions involving hydrogens, halogens, chalcogens, pnictogens and so forth [1–6]. According to the AIM formalism, a bonding interaction between two atoms is signified by the existence of a bond path linking the associated nuclei, eventually leading to an energetic stabilization as a bond path is always mirrored by a single line of maximally negative potential energy density connecting the same nuclei, known as the virial path [2–6]. Conversely, another school of scientists consider the existence of a bond path between two nuclei as an indication of interaction between them which could even be repulsive i.e. destabilizing in nature [7–10]. The aforesaid controversy; especially with respect to the HH interaction in planar biphenyl, led to a series of heated scientific arguments, thereby imposing the conundrum of assigning an unambiguous relationship between bond path and chemical bonding [11–16]. Furthermore, though the existence of intra- and intermolecular ‘‘short contact” closed-shell interactions between electronegative atoms, especially between oxygens (OO) and halogens (XX, where X = F, Cl, Br, I) is well-documented in crystallography, receiving comprehensive support from theoretical analyses [17–21]; associated energetics is still inadequately understood. The aim of the present contribution is to attempt for a meticu- lous AIM-based theoretical analysis of the molecular forces present within and hence to decipher their critical roles in governing the local/global stabilization of the molecular system 3-Hydroxy-2- pyridin-2-yl-propenal, henceforth abbreviated as HPYP; which offers a molecular framework consisting of a miscellany of non- covalent interactions. The present study also underpins the neces- sity of Nucleus Independent Chemical Shift (NICS) analysis [22] toward drawing a comprehensive conclusion on the stability of HPYP, which in turn dictates the regulatory role of aromaticity underlying the overall stabilization of the framework. At this point, it is to be emphasized that the present case study involving HPYP does not claim to approach a generalized view- point on the long-debated issue(s), rather provides a specific exam- ple in which we have shown (i) the interplay of aromaticity and the http://dx.doi.org/10.1016/j.comptc.2017.08.004 2210-271X/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. E-mail addresses: ani.physichem@gmail.com (A. Ganguly), nguchhait@yahoo. com (N. Guchhait). Computational and Theoretical Chemistry 1117 (2017) 108–118 Contents lists available at ScienceDirect Computational and Theoretical Chemistry journal homepage: www.elsevier.com/locate/comptc