Aromaticity in heterocyclic analogues of benzene: comprehensive analysis of structural aspects, electron delocalization and magnetic characteristics

Abstract

The degree of aromaticity of six-membered monoheterocycles with IV -VI group heteroatoms (C 6 H 5 X, where X=SiH, GeH, N, P, As, O + , S + , Se + ) was analyzed using the results of ab initio calculations at the MP2/cc-pvtz level. Values of common aromaticity indices including those based on electronic delocalization properties, structural-dynamic features and magnetic properties all indicate high aromaticity of all considered heterocycles.A decrease in aromaticity is observed with increasing atomic number of the heteroatom, except in the case of the pyrylium cation. However, not all types of indices or even different indices within the same type correlate well among each other. Ring currents have been obtained at the HF/cc-pvdz level using the ipsocentric formulation. Ring current maps indicate that in the case of cationic heterocycles the ring current persists in all molecules under consideration. The different conclusions reached depending on the type of index used, are a manifestation of the fact that when not dealing with hydrocarbons, aromaticity is illdefined. One should always express explicitly which property of the molecules is considered to establish a degree of "aromaticity".

A DFT Study on the Stability and Aromaticity of Heterobenzenes Containing Group 15 Elements

“…To compute the enthalpies of formation of the heterobenzenes, the reaction energy for all reaction schemes (1)- (11) was computed using the following equation [23]:…”

“…The present paper deals with the evaluation of aromaticity of mono-, di-, tri, tetra-, penta-, and hexasubstituted heterobenzenes with N, P, and As atoms (see Fig. Literature survey reports experimental and theoretical studies regarding the heteroanalogues of benzene where one or more CH units are replaced by isovalent species [8][9][10][11][12]. Literature survey reports experimental and theoretical studies regarding the heteroanalogues of benzene where one or more CH units are replaced by isovalent species [8][9][10][11][12].…”

“…Enthalpies of Formation, H f (kcal/mol), Calculated at the B3LYP/6-311+G(d,p) Level of Theory from Reactions (1)-(11).…”

Aromaticity in heterocyclic analogues of benzene: Dissected NICS and current density analysis

“…In 2011, the groups of Shishkin and Bultinck evaluated the aromatic character in a series of monoheterocycles, analogues of benzene, containing Group 13 to 16 elements (C 5 H 5 X, where X = SiH, GeH, N, P, As, O + , S + , Se + ) . They used a total of 10 quantitative indexes (based on structural, magnetic, energetic, and electronic properties of the aromatic rings) and compared the aromaticity trends throughout the series.…”

Aromaticity of benzenoid hydrocarbons with inserted –B=B– and –BH–BH– groups: a comparison

“…Replacement of one or more carbon atom(s) in benzene and in polycyclic aromatic hydrocarbons (PAH) by heteroatoms other than the typical ''heterocyclic'' elements like nitrogen, oxygen, phosphorus and sulfur has been recently a topic of several studies [1][2][3][4][5][6]. Such structural modifications are important because they can create compounds with unusual properties.…”