On the performance of resonance assisted hydrogen bond theory in malonaldehyde derivatives Ebrahim Nakhaei a , Alireza Nowroozi b,⇑ a Department of Chemistry, Payame Noor University, Tehran, Iran b Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran article info Article history: Received 2 July 2016 Received in revised form 23 September 2016 Accepted 23 September 2016 Keywords: Malonaldehyde Intramolecular hydrogen bond P-electron delocalization Aromaticity indices AIM NBO abstract According to the resonance assisted hydrogen bond (RAHB) theory, the p-electron delocalization (p-ED) promotes the intramolecular hydrogen bond (IMHB). Since the relation between the IMHB and p-ED are not well known, in the present work, the linear correlations between the descriptors of p-ED and esti- mated IMHB energies were systematically investigated. In this regard, the significance of p-ED in che- lated forms of the benchmark systems by various descriptors, such as k, k 0 , HOMA, NICS, PDI, ATI, FLU and FLUp were evaluated. On the other hand, the IMHB energy of RAHB units by some adopted models, such as RRM, RBM, GCM, IRM and OCM are estimated. Furthermore, we explored all of the possible linear correlations between the p-ED indices and various IMHB energies to judge about the performance of RAHB theory. According to our results, it was found that there are great liner correlations between the RRM, RBM and GCM than IRM and OCM methods with some of the p-electron delocalization indices; RRM: k 0 > FLU > k > HOMA > FLUp  ATI > PDI > NICS(1) > NICS(0) RBM: k 0 > k > HOMA > FLU > FLUp > ATI > PDI > NICS(1) > NICS(0) GCM: k 0  HOMA > k > PDI > FLU > FLUp > NICS(1) > ATI > NICS(0). Surprisingly, the bond order factor of Gilli (k 0 ), which introduced similar to k, has the best linear relation- ship with the IMHB energies. Consequently, the linear coefficients between the RRM, RBM and GCM ener- gies with HOMA, k and k 0 descriptors are in agreement with the RAHB theory. Ó 2016 Published by Elsevier B.V. 1. Introduction It is well known that non-covalent interactions play a central role in all aspects of physical science [1]. The hydrogen bond is one of the most important categories of non-covalent interactions and it is not surprising that many attempts, experimentally or the- oretically, have been made to describe the nature of hydrogen bonds [2–6]. According to the systematic investigation of struc- tural and spectroscopic data Gilli and coworkers was classified the hydrogen bonds to different categories: resonance assisted hydrogen bonds (RAHBs), charge assisted hydrogen bonds (±CAHBs) and low barrier hydrogen bonds (LBHBs) [7]. The reso- nance assisted hydrogen bond (RAHB) is a special type of hydrogen bonds that benefits from a resonance phenomenon in the molecu- lar framework and classified to the inter and intramolecular cases [7]. The X-ray and spectroscopic data of b-dicarbonyl compounds indicate that with shortening of OAHO distance, the chemical shift of enolic proton d(OH) increased and OAH stretching fre- quency decreased. According to these data, the authors suggested that the resonance process, through the p-conjugated double bonds, can be stabilizing the cis enol forms of these compounds and assist the hydrogen bond. Over the years, the RAHB model has become a widely accepted and applied to understand the nature of hydrogen bonding in a broad range of benchmark systems, especially for OAHO hydro- gen bond in malonaldehyde and its derivatives [8–12]. However, in the past decade Yanez et al. have published a series of papers and questioning the validity of RAHB idea [13–16]. They investigated a vast selection of compound, such as b-dicarbonyl and b- enaminone, and concluded that there is no evidence of resonance assisting to intramolecular hydrogen bonds. Because of controver- sies in physical origin of the intramolecular resonance assisted hydrogen bonded systems, in the present study we decide to per- form a comprehensive theoretical study about the RAHB systems in malonaldehyde derivatives. The main goals of this study are as follows: http://dx.doi.org/10.1016/j.comptc.2016.09.029 2210-271X/Ó 2016 Published by Elsevier B.V. ⇑ Corresponding author. E-mail address: anowroozi@chem.usb.ac.ir (A. Nowroozi). Computational and Theoretical Chemistry 1096 (2016) 27–32 Contents lists available at ScienceDirect Computational and Theoretical Chemistry journal homepage: www.elsevier.com/locate/comptc