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.

Substituents and environment influences on aromaticity of peri- and para-substituted naphthalenes.

The influence of substituents and environment on the aromaticity of the naphthalene ring is shown for a series of peri- and para-substituted naphthalenes. Crystal structure geometries are compared with the single molecule structures in vacuum (optimized at the B3LYP/6-311++G** level) and with structures determined in media of different polarity. The harmonic oscillator model of aromaticity (HOMA) index of the naphthalene rings has been used to characterize the aromaticity of the investigated molecules.

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 ΔP 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.

Keto forms of salicylaldehyde Schiff bases: structural and theoretical aspects.

Twelve Schiff bases of methoxy-substituted salicylaldehyde have been examined by crystallographic and spectroscopic methods, as well as by DFT theoretical calculations in order to investigate the effect of the substituent's position on the keto-enol equilibrium in the crystalline state. Four out of the 10 structurally characterized compounds with methoxy substitution on the para and/or ortho positions with respect to the aldimine bridge and deriving from aliphatic amines or alkylarylamines are found as cis-keto tautomers and form dimers. In contrast, the five pure enol tautomers derive either from aliphatic or alkylarylamines and are meta substituted or from aniline or benzylamine and are para and/or ortho methoxy substituted.

Chemistry, photophysics, and ultrafast kinetics of two structurally related Schiff bases containing the naphthalene or quinoline ring.

The two structurally related Schiff bases, 2-hydroxynaphthylidene-(8-aminoquinoline) (HNAQ) and 2-hydroxynaphthylidene-1(')-naphthylamine (HNAN), were studied by means of steady-state and time resolved optical spectroscopies as well as time-dependent density functional theory (TDDFT) calculations. The first one, HNAQ, is stable as a keto tautomer in the ground state and in the excited state in solutions, therefore it was used as a model of a keto tautomer of HNAN which exists mainly in its enol form in the ground state at room temperature. Excited state intramolecular proton transfer in the HNAN molecule leads to a very weak (quantum yield of the order of 10(-4)) strongly Stokes-shifted fluorescence.

DFT studies of the structure and vibrational spectra of 8-hydroxyquinoline N-oxide.

The geometry, frequency and intensity of the vibrational bands of 8-hydroxyquinoline N-oxide (8-HQNO) and its deuterated derivative (8-DQNO) were obtained by the density functional theory (DFT) with the BLYP and B3LYP functionals and 6-31G(d,p) basis set. The optimized bond lengths and bond angles are in good agreement with the X-ray data. The IR and INS spectra of 8-HQNO and 8-DQNO computed at the DFT level reproduce the vibrational wavenumbers and intensities with an accuracy, which allows reliable vibrational assignments.

The 15N and 13C solid state NMR study of intramolecular hydrogen bond in some Schiff's bases.

A series of 11 Schiff's bases derived from substituted salicylaldehyde and aliphatic amines has been studied in the solid state by 15N and 13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR). 15N CPMAS is especially useful for investigation of the tautomerism in the compounds considered, owing to the large difference in the nitrogen chemical shifts of OH and NH tautomers. In the solid state, three of the compounds examined were shown by 15N NMR to exist as OH tautomeric forms, and the remaining eight as the corresponding NH forms.