Michał A. Dobrowolski

Interplay of π-Electron Delocalization and Strain in [n](2,7)Pyrenophanes

The geometries of a series of [n](2,7)pyrenophanes (n = 6-12) were optimized at the B3LYP/6-311G** DFT level. The X-ray crystal structures determined for the [9](2,7)- and [10](2,7)pyrenophanes agreed excellently with the computed structures. The degree of nonplanarity of the pyrene moiety depends on the number of CH2 groups in the aliphatic bridge and, as analyzed theoretically, influences the strain energy and the extent of pi-electron delocalization in the pyrene fragment. Various indices, e.g., the relative aromatic stabilization energies (DeltaASE), magnetic susceptibility exaltations (Lambda), nucleus-independent chemical shifts (NICS), and the harmonic oscillator model of aromaticity (HOMA) were used to quantify the change in aromatic character of the pyrene fragment. DeltaASE and relative Lambda values (with respect to planar pyrene) were evaluated by homodesmotic equations comparing the bent pyrene unit with its bent quinoid dimethylene-substituted analog. The bend angle, alpha, DeltaASE, and Lambda were linearly related. The aromaticity decreases smoothly and regularly over a wide range of bending, but the magnitude of the change is not large. The differences between planar pyrene (alpha = 0 degrees) and the most distorted pyrene unit (alpha = 39.7 degrees in [6](2,7)pyrenophane) are only 15.8 kcal/mol (DeltaASE) and 18.8 cgs-ppm (Lambda). Also, the geometry-based HOMA descriptor changes by only 0.07 unit. The local NICS descriptors of aromatic character also correlate very well with the global indices of aromaticity. In line with the known reactivity of pyrenophanes, the variations of NICS(1), a measure of pi-electron delocalization, were largest for the outer, biphenyl-type rings. The strain energies of the pyrene fragments were much larger and varied more than those evaluated for the bridge. Both strain energies were interrelated (correlation coefficient R = 0.979) and depend on the bend angle, alpha.

On the aromatic stabilization energy of the 4N π electron pyrene

The aromatic stabilization energy (ASE) of pyrene, evaluated with both isodesmic equation and ab initio valence bond (VB) theory-based block localized wavefunction (BLW) methods, gives consistent results (ca 74 kcal/mol). Biphenyl, phenanthrene and benzene, evaluated similarly, all have essentially the same ASEs per ring carbon. The aromaticity of pyrene is not diminished because of its 4n π electron count.

Structural diversities of charge transfer organic complexes. Focus on benzenoid hydrocarbons and 7,7,8,8-tetracyanoquinodimethane

We have obtained three-component systems: the complexes comprising of two different benzenoid hydrocarbons together with one molecule of 7,7,8,8-tetracyanoquinodimethane (TCNQ). The X-ray single-crystal structures of naphthalene–perylene–TCNQ and pyrene–perylene–TCNQ revealed that they form face-to-face stacking between perylene and TCNQ molecules containing another hydrocarbon as a guest in the structure. We also present a pyrene–TCNQ complex with two pyrene moieties acting in similar way. In this system, charge transfer is far more efficient than in any other complexes of TCNQ with benzenoid hydrocarbons. Additionally, we have also obtained as references pyrene–TCNQ, chrysene–TCNQ, phenanthrene–TCNQ and naphthalene–TCNQ with 1 : 1 molecular ratios. These systems were also used to estimate the degrees of charge transfer.

Are Thermodynamic and Kinetic Stabilities Correlated? A Topological Index of Reactivity toward Electrophiles Used as a Criterion of Aromaticity of Polycyclic Benzenoid Hydrocarbons

A topological index of reactivity (TIR) of benzenoid hydrocarbons is defined basing on an approximate value of the bicentric localization energies. TIR values correlate with all known (24) Hammett-Streitwieser position constants, based on kinetic data for electrophilic substitution in benzenoid hydrocarbons. The maximum value of the index, denoted by TIR(max), defines the stability of a molecule toward electrophiles. For all 35 nonisoarithmic molecules of benzenoid hydrocarbons for which Hess and Schaad data are known, TIR(max) values correlate with classical numerical characteristics of aromaticity: resonance energy per pi-electron (REPE), HOMO-LUMO gap, and geometry based aromaticity index HOMA. Correlation between TIR(max) and exaltation of magnetic susceptibility is also found for cata-condensed benzenoid hydrocarbons, whereas if the peri-condensed ones are included, no correlation is observed. This can be ascribed to the presence of both paratropic and diatropic rings in perifusenes.

On the aromatic stabilization of corannulene and coronene

The application of set of homodesmotic reactions allowed us to estimate the aromatic stabilization energy (ASE) of corannulene and coronene. Appropriate reactions have been applied to balance syn/anti mismatches in di-, tetra- and hexamethylene substituted derivatives. Based on many different polycyclic reference structures that compensate the effect of strain in the corannulene moiety the value of ASE comes to 44.5 kcal mol(-1). Planar corannulene is more stabilized by cyclic π-electron delocalization by ca. 10.7 kcal mol(-1), as compared with a bowl-shaped system. A similar approach for coronene leads to an ASE equal to 58.4 kcal mol(-1).

Synthesis and structure evaluation of new complex butylarylpiperazin-1-yl derivatives

AbstractA series of arylpiperazine derivatives of 1,16-diphenyl-19-azahexacyclo-[14.5.1.02,15.03,8.09,14.017,21]docosa-2,3,5,7,8,9,11,13,14-nonaene-18,20,22-trione and 4,10-diphenyl-1H,2H,3H,5H-indeno[1,2-f]isoindole-1,3,5-trione was synthesized. The pharmacological profile of compound 4 at the 5-HT1A receptor was measured by binding assay. The title compounds were tested in cell-based assay against the human immunodeficiency virus type-1. The X-ray crystallographic studies of derivatives 2, 6, 7, 11, 19, and 20 were presented.

6-Bromo-2-methyl-sulfanyl-1,3-benzo-thia-zole.

The title molecule, C8H6BrNS2, is almost planar with a dihedral angle of 0.9 (1)° between the benzene and thiazole rings. The values of the geometry-based index of aromaticity (HOMA) and the nucleus-independent chemical shift (NICS) for the two cyclic fragments of the title molecule are 0.95 and −9.61, respectively, for the benzene ring, and 0.69 and −7.71, respectively, for the thiazole ring. They show that the benzene ring exhibits substantially higher cyclic π-electron delocalization than the thiazole ring. Comparison with other similar benzothiazole fragments reveals a similar trend.