Geometric Aspects of Aromaticity: Interrelations between Intramolecular Hydrogen Bonds, Steric Effects and π‐Electron Delocalisation in Nitroanilines

Abstract

The influence of intramolecular hydrogen bonds and steric hindrance on distortion from planarity of the benzene ring and its aromaticity is shown for a series of substituted 2,4,6‐trinitroanilines. The crystal structure geometry and thegeometry optimized at the B3LYP/6‐311++G** level are compared with analogues without intramolecular hydrogen bonds. The HOMA index and the parameter ΔP describing the distortion from planarity of the benzene ring were used to characterize the aromacity of the investigated molecules. NBO and AIM analysis were also applied.

Aromaticity and Through-Space Interaction between Aromatic Rings in [2.2]Paracyclophanes

“…To our knowledge, no systematic research on a relationship between distortion from planarity and decrease of aromaticity for a family of substituted [2.2]­paracyclophanes has been done yet. We compare the HOMA aromaticity index with the nonplanarity parameter Δ P for the experimental structures of [2.2]­paracyclophanes collected in the CSD databases …”

Aromaticity of benzene derivatives: an exploration of the Cambridge Structural Database

“…A significant decrease in aromaticity was found for several overcrowded 2,4,6-trinitroanilines (Majerz & Dziembowska, 2011.…”

“…This effect results from a through-resonance interaction and increasing participation of a quinoid resonance structure (Krygowski & Stę pień , 2005;Dobrowolski et al, 2009;Szatylowicz, Siodla et al, 2016). Very low to negative HOMA values were found for some overcrowded nitro-amino derivatives (Omelchenko et al, 2012;Majerz & Dziembowska, 2011. It was shown that the factors responsible for reduction down to anti-aromaticity were the formation of an intramolecular NHÁ Á ÁO hydrogen bond between the amino and nitro groups as well as considerable deviation from planarity of the aromatic ring caused by steric interaction between the bulky groups substituted onto the benzene ring.…”

“…Despite numerous papers devoted to the effect of substituents on aromaticity, only a few investigations on solid-state benzene derivatives have been performed Majerz & Dziembowska, 2011Cyrań ski & Krygowski, 1996).…”

Aromaticity and stability going in opposite directions: An energetic, structural, magnetic and electronic study of aminopyrimidines

“…On the other hand, as the bonds elongate and became weaker, the aromaticity of the rings also decreases, and this is the energetic contribution to de-aromatization. Majerz and Dziembowska [23], recently, have shown that intramolecular hydrogen bonds, steric effects and p-electron delocalization strongly influences the HOMA values. In this study, besides these effects, it will be shown that symmetry can also have a biased influence on the evaluation of aromaticity by this criterion and, to the best of our knowledge this has not yet been spotted in other studies.…”