Aromaticity of <i>peri</i>- and <i>para</i>-Substituted Naphthalene-1-carbaldehyde. Comparison with 1‑Nitronaphthalene

Aromaticity of the naphthalene ring substituted by formyl or nitro and secondary amine groups in <i>peri</i> and <i>para</i> positions has been investigated. HOMA (harmonic oscillator model of aromaticity) index of the naphthalene rings has been used to characterize the aromaticity of the investigated molecules. Ellipticity of C2–C3 (C6–C7) bonds, obtained by means of topological analysis of the electron density, has been used as a measure of the through-resonance effect between the <i>para</i> substituents. Dependence of the HOMA values on the rotation angle of formyl and nitro groups to the aromatic plane for naphthalene-1-carbaldehyde and their derivatives with dimethylamino group in <i>para</i> position has been analyzed. It has been shown that the nitro group has a stronger resonance effect and causes greater decrease of aromaticity than the formyl group only for planar or close to planar conformation. The attractive and repulsive <i>peri</i> interactions have been analyzed by using the QTAIM and NCI methods. Interrelation between the <i>peri</i> and <i>para</i> interactions has been discussed

Aromaticity of Overcrowded Nitroanilines

For a series of 2,4,6-trinitroanilines substituted with bulky groups, the influence of intramolecular hydrogen bonds, electronic substituents effect, and steric hindrance on aromaticity of the molecules in crystals and their analogues optimized at the B3LYP/6-311++G** level were studied. The HOMA index was used as a measure of the aromaticity, while the parameter Δ<i>P</i> was a description of the distortion of the benzene ring from planarity. Conformation of the nonplanar ring in crystal and optimized structures was also described using the puckering parameters. A comparison of the data for crystal and optimized structures showed an important effect of the intermolecular interactions on aromaticity of the overcrowded nitroanilines. The packing effects were analyzed using the simplified PCM model of solvents. NBO analysis illustrated the changes of orbitals upon dearomatisation

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

The HOMA index calculated for [2.2]­paracyclophanes in the solid state reveals a slight decrease of aromaticity. Interactions between aromatic rings of [2.2]­paracyclophane have been investigated using AIM and NCI analysis in both crystal and optimized [2.2]­paracyclophane structures. AIM analysis showed that the C···C bond path between the two aromatic rings is present only in few [2.2]­paracyclophanes. The NCI approach visualized the dispersion and repulsive interactions between the aromatic rings of every [2.2]­paracyclophane. Combination of AIM and the NCI approach is necessary for determining and identifying nonbonded interactions in [2.2]­paracyclophanes