Heteroatom Chemistry Volume 26, Number 3, 2015 A DFT Study on the Stability and Aromaticity of Heterobenzenes Containing Group 15 Elements Iulia P ˘ aus ¸escu, 1,2 Mihai Medeleanu, 1 Mircea S ¸ tef ˘ anescu, 1 Francisc Peter, 1 and Raluca Pop 3 1 Faculty of Industrial Chemistry and Environmental Engineering, University Politehnica of Timis ¸oara, 300006, Timis ¸oara, Romˆ ania 2 Institute for Chemistry Timis ¸oara of the Romanian Academy, 300223, Timis ¸oara, Romˆ ania 3 Faculty of Pharmacy, University of Medicine and Pharmacy “Victor Babes ¸” Timis ¸oara, 300041, Timis ¸oara, Romˆ ania Received 14 August 2014; revised 15 October 2014 ABSTRACT: The stability and aromaticity of 36 het- erobenzenes containing group 15 elements were evalu- ated at the B3LYP/6-311+G(d,p) level of theory. Stabil- ity evaluation was performed based on the enthalpies of formation calculated from imaginary reactions and on the absolute hardness reactivity descriptor. The aro- maticity was investigated by means of geometric (Bird, Harmonic Oscillator Model of Aromaticity (HOMA) indices), energetic (aromatic stabilization energy), and magnetic criteria (nucleus-independent chemi- cal shifts [NICS] index). Also, within the concep- tual density functional theory (DFT) theory, reactivity- based descriptors (highest occupied molecular orbital and lowest unoccupied molecular orbital [HOMO— LUMO] energy gap, absolute hardness, electrophilic- ity) were computed. The results led to the conclusion that all heterobenzenes exhibit aromatic character, which generally decreases from N to As contain- ing compounds and from one to six substituted CH groups. C  2014 Wiley Periodicals, Inc. Heteroatom Chem. 26:206–214, 2015; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21250 Correspondence to: Mihai Medeleanu; e-mail: mihai.medeleanu @upt.ro. Supporting Information is available in the online issue at www.wileyonlinelibrary.com. C  2014 Wiley Periodicals, Inc. INTRODUCTION Aromaticity is a fundamental concept in organic chemistry and plays an important role in determin- ing the structure, stability, and reactivity of many molecules [1]. Although aromaticity is a frequently used term, there is no generally accepted definition of it [2, 3] and the numerous studies that have been performed in this regard use various quantifying cri- teria. It is well recognized that aromaticity is both a qualitative and quantitative concept [4], and cur- rently the most frequently used quantitative mea- sures to evaluate aromaticity can be classified as geometric, energetic, and magnetic criteria. There are also electronic descriptors within the conceptual density functional theory (DFT) theory that can be used in the study of aromaticity [1]. However, owing to its elusive character, precise quantification has proven to be a challenge. The geometric criteria of aromaticity are based on bond lengths, bond orders, and bond angles equalization and planarity (if applicable). The en- ergetic criteria use aromatic systems that have a high chemical stability compared with their chain analogues. Therefore, when using this criterion, one compares the excess of stability of the structure due to the cyclic electron delocalization relative to a well-chosen reference system, in most cases olefins or conjugated polyenes [2]. The magnetic cri- teria of aromaticity are based on the ability of an 206