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The elusiveness of hexazine (a.k.a. hexaazabenzene) and its perhydrogenated derivative, hexazinane, prompted the author of this paper to investigate the possibility of stabilizing the six-membered nitrogen ring by inserting it into [18]-annulene. The resulting compound is made of a central N6 ring surrounded by an outer ring of 18 carbon atoms that prevents its decomposition into dinitrogen. The N6 ring is non-planar and with a chair-like conformation that does not undergo conformational isomerization. The designed molecule can be stabilized either by oxidation to a hexa-oxide derivative or by coordination of ZnCl+. Furthermore, a triangle-shaped macrocyclic isomer made of three pyridazine moieties connected to each other by ethylene bridges represents a possible precursor in the synthesis of the N6-embedded hydrocarbon. By employing an alkali or alkaline-earth metal cation that coordinates the three pyridazine monomers it becomes possible to bring their nitrogen atoms in close proximity so that a subsequent aromatic fusion reaction could be attempted. [ABSTRACT FROM AUTHOR]

The cyclopentenium carbocation, cyclo-C5H7+ or CP+, and eight cyclic isomers were computationally investigated with quantum chemistry methods. These nine isomers display a significant structural diversity: three have a five-membered ring, four have a four-membered ring, and other two have a three-membered ring. The most stable isomer after CP+ is the dimethyl-cyclopropenium cation which is a 2 π aromatic molecule. The vibrational spectra of the nine cyclic isomers were simulated and the normal modes associated to the most intense peaks were identified. The charge distribution in the cyclic carbocations was explored with the quantum theory of atoms in molecules (QTAIM). It appears that the less stable isomers have in their rings either one carbon atom with a large negative charge or two/three linked carbon atoms with a small negative charge. Neutral derivatives of type CP-R (R = H, F, Cl, Br, I, and OH) were also investigated since they represent potential precursors in the large-scale generation of CP+. Among them, 3-iodo-cyclopentene is the precursor with the lowest bond dissociation enthalpy for the heterolytic rupture of the C–R bond. [ABSTRACT FROM AUTHOR]

The gas-phase electron diffraction (GED) study of tri-tert-butyl methane (TTBM) published in 1972 by Bürgi and Bartell inspired the author to investigate the nature of the intramolecular interactions that are operative in this crowded hydrocarbon. Using the quantum theory of atoms in molecules (QTAIM), a topological analysis of the theoretical charge density of TTBM is carried out. Nine bond paths corresponding to the presence of noncovalent, intramolecular interactions operating at the interfaces that separate the three t-Bu groups do emerge from the QTAIM analysis. This result supports the existence of a network of intramolecular interactions predicted by Bürgi and Bartell in their landmark GED study of TTBM. In addition, the not yet synthesized halogen analogues (t-Bu)3 CX (X=F to I) are also investigated herein. Some information about the remarkable contributions of the pioneers is provided throughout the paper. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations, we investigate the geometries and electronic structures of the perhalogenated derivatives of boric acid, XBO (with X = halogen). These molecules in their low-energy states are C symmetric with a shape that resembles a triskelion, an ancient symbol that appears inside the flags and coat of arms of countries, regions, and cities throughout Europe. The molecular triskelions can form polar complexes with ammonia which are stabilized by a dative bond between nitrogen and boron, while a second type of adducts arises from the halogen bonding between nitrogen and the terminal halogen atom. By virtue of their different HOMO-LUMO gaps, the molecular triskelions and their complexes with ammonia might provide novel bulk materials where the band gap can be tuned simply by changing the type of halogen bonded to the BO moiety. [ABSTRACT FROM AUTHOR]