The partitioning of space with Hirshfeld surfaces enables the analysis of fingerprint molecular interactions in crystalline environments. This study uses the decomposition of the crystal contact surface between pairs of interacting chemical species to derive an enrichment ratio. This quantity enables the analysis of the propensity of chemical species to form intermolecular interactions with themselves and other species. The enrichment ratio is obtained by comparing the actual contacts in the crystal with those computed as if all types of contacts had the same probability to form. The enrichments and contact tendencies were analyzed in several families of compounds, based on chemical composition and aromatic character. As expected, the polar contacts of the type H...N, H...O and H...S, which are generally hydrogen bonds, show enrichment values larger than unity. O...O and N...N contacts are impoverished while H...H interactions display enrichment ratios which are generally close to unity or slightly lower. In aromatic compounds, C...C contacts can display large enrichment ratios due to extensive π...π stacking in the crystal packings of heterocyclic compounds. C...C contacts are, however, less enriched in pure (C,H) hydrocarbons as π...π stacking is not so favourable from the electrostatic point of view compared with heterocycles. C...H contacts are favoured in (C,H) aromatics, but these interactions occur less in compounds containing O, N or S as some H atoms are then involved in hydrogen bonds. The study also highlights the fact that hydrogen is a prefered interaction partner for fluorine.

Numerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect. The substituent effect of the nitro group may be well described using either traditional substituent constants or characteristics based on quantum chemistry, i.e., cSAR, SESE, and pEDA/sEDA models. Interestingly, the cSAR descriptor allows to describe the electron-attracting properties of the nitro group regardless of the position and the type of system. Analysis of classical and reverse substituent effects of the nitro group in various systems indicates strongpi-electron interactions with electron-donating substituents due to the resonance effect. This significantly affects thepi-electron delocalization of the aromatic ring decreasing the aromatic character, evidenced clearly by HOMA values. Use of the pEDA/sEDA model allows to measure the population of electrons transferred from the ring to the nitro group.

An application of a charge of the substituent active region concept to 1-Y,4-X-disubstituted derivatives of bicyclo[2.2.2]octane (BCO) [where Y = NO₂, COOH, OH, and NH₂ and X = NMe₂, NH₂, OH, OMe, Me, H, F, Cl, CF₃, CN, CHO, COMe, CONH₂, COOH, NO₂, and NO] provides a quantitative information on the inductive component of the substituent effect (SE). It is shown that the effect is highly additive but dependent on the kind of substituents. An application of the SE stabilization energy characteristics to 1,4-disubstituted derivatives of BCO and benzene allows the definition of inductive and resonance contributions to the overall SE. Good agreements with empirical approaches are found. All calculations have been carried out by means of the B3LYP/6-311++G(d,p) method.

Structural parameters of a range of over 100 meso-substituted zinc porphyrins were reviewed and compared to show how far the nature of the functional group may affect the interatomic distances and bond angles within the porphyrin core. It was proved that even despite evident deformations of the molecular structure, involving twisting of the porphyrin's central plane, the coupled π-bonding system remains flexible and stable. DFT calculations were applied to a number of selected porphyrins representative for the reviewed compounds to emphasize the relevance of theoretical methods in structural investigations of complex macrocyclic molecular systems. Experimental and DFT-simulated IR spectral data were reported and analyzed in context of the individual molecular features introduced by the meso substituents into the porphyrin moiety base. Raw experimental spectral data, including ¹H- and ¹³C-NMR, UV-Vis, FTIR, XRD, and other relevant physicochemical details have been provided for a specially chosen reference zinc porphyrin functionalized by tert-butylphenyl groups.