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A number of hexaarylbenzene compounds were studied theoretically, in order to compare energy changes as a result of the toroidal delocalization effect that is characteristic of all these species. The energy was studied taking advantage of locally designed isodesmic reactions. Results indicate that the amount of aromaticity manifested by each substituent is a factor that should be considered when assessing the quantity of energy dissipated from each aromatic center. The influence of different substituents on electronic delocalization is also analyzed, as well as the role played by their frontier molecular orbitals.

The synthesis of a new type of pentacyclic benzothiazolium compound -6,13-dihydropyrazino[2,1-b:5,4-b´]bis(1,3-benzothiazole)-7,14-diiumdibromide (2), is reported. Compound 2 was prepared by dimerization of 2-(bromomethyl)benzothiazole. Quantum chemical calculation studies have been carried out on the structures of possible isomers of 2, as well as the products of its deprotonation reactions.

Ab initio calculations have been performed on the (CO) n (CO 2 ) m cyclic copolymers, where n , m =1,2 with m ≥ n . The cyclic molecules were studied at the HF/6-311G, HF/6-311+G(df), MP2/6-311+G(df) levels and Gaussian-2 theory with reduced Moller–Plesset order, G2MP2. The structures of the three cyclic oligomers investigated, C 2 O 3 , C 3 O 5 and C 4 O 6 are found to have a minimum and the geometries are planar. The energy releases of the dissociation reactions indicate that these molecules are thermodynamically unstable with respect to the parent monomers CO and CO 2 . In addition, the heats of formation for the cyclic molecules were evaluated at the G2MP2 level using an isodesmic approach and bond separation energies.

The energies of combustion and fusion of 5-cyano-5H-dibenzo[a,d]cycloheptene (1) and (5E,11E)-dibenzo[a,e]cyclooctene-5,11-dicarbonitrile (2) were measured by means of microbomb calorimetry and DSC, respectively. The derived enthalpies of formation in solid state are 320 ± 18 for nitrile 1 and 470 ± 31 kJ mol−1 for nitrile 2, respectively. The experimental enthalpies of formation are discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory, by means of group additivity and isodesmic reactions. The two nitriles are not stabilized by dibenzoannelation.