What Is the Main Feature Distinguishing the Through-Space Interactions in Cyclophanes from Their Aliphatic Analogues?

Classical cyclophanes with two benzene rings have been compared with cyclophanes with one benzene ring replaced with an aliphatic part and aliphatic compounds, which are cyclophane analogues. Analysis of geometry, atomic charges, and aromatic and steric energy and investigation of intramolecular noncovalent interactions and charge mobility show that there is no special feature that distinguishes the classical cyclophanes from aliphatic analogues, so the definition of cyclophanes can be extended to other compounds.

Substituent effect on inter-ring interaction in paracyclophanes.

The theoretical calculations, namely multipole-derived charge analysis, quantum theory of atom in molecules, and non-bonding interaction (NCI), were performed for [2.2]paracyclophanes, [2.2]paracyclophane-7,9-dienes, and [3.

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

The harmonic oscillator model of aromaticity (HOMA) index, one of the most popular aromaticity indices for solid-state benzene rings in the Cambridge Structural Database (CSD), has been analyzed. The histograms of HOMA for benzene, for benzene derivatives with one formyl, nitro, amino or hydroxy group as well as the histograms for the derivatives with two formyl, nitro, amino or hydroxy groups in ortho, meta and para positions were investigated. The majority of the substituted benzene derivatives in the CSD are characterized by a high value of HOMA, indicating fully aromatic character; however, the distribution of the HOMA value from 1 to about 0 indicates decreasing aromaticity down to non-aromatic character.

Aromaticity of peri- and para-Substituted Naphthalene-1-carbaldehyde. Comparison with 1-Nitronaphthalene.

Aromaticity of the naphthalene ring substituted by formyl or nitro and secondary amine groups in peri and para 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 para substituents.

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.