corannulene and sumanene

Nucleus independent chemical shift (NICS) criterion was used to gauge the amount of aromaticity in a lot of publications in two last decades. Non-planar molecules with many polygons in different sheets that make angle together have not been studied by this criterion. Perhaps, one ascribes this deficiency to NICS index, but we think it is concern to depauperation in evaluation methods. Therefore, in this work, we try to evaluate aromaticity of two fullerene substructures bowl-shaped molecules, namely corannulene and sumanene as typical non-planar molecules by using of the NICSzz-scan method. The gauge-independent atomic orbital (GIAO) NMR calculations were done at B3LYP/6-311+G(d) level of theory. Energetic criterion as another tool for evaluation of the aromaticity of compounds was used and discussed. Results shows that pentagon and hexagon rings in corannulene have antiaromatic and aromatic character, respectively and in sumanene, pentagon and outer hexagon rings have antiaromatic and aromatic character, respectively. However, the picture obtained based on the NICS computations did not provide any insight towards the real nature of current density in the corannulene and sumanene.

Topics: Fullerenes; Hydrophobic and Hydrophilic Interactions; Molecular Structure; Polycyclic Aromatic Hydrocarbons; Quantum Theory; Thermodynamics

Complexes formed by substituted buckybowls derived from corannulene and sumanene with sodium cation or chloride anion have been computationally studied by using a variety of methods. Best results have been obtained with the SCS-MP2 method extrapolated to basis set limit, which reproduces the highest-level values obtained with the MP2.X method. All bowls form stable complexes with chloride anion, with stabilities ranging from -6 kcal/mol in the methylated corannulene derivative to -45 kcal/mol in the CN-substituted sumanene. The opposite trend is observed in sodium complexes, going from deeply attractive complexes with the methylated derivatives (-36 kcal/mol with sumanene derivative) to slightly repulsive ones in the CN-substituted bowls (2 kcal/mol in the corannulene derivative). Anion complexes are stabilized by large electrostatic interactions combined with smaller though significant dispersion and induction contributions. Conversely, cation complexes are stabilized by large induction contributions capable of holding together the bowl and the cation even in cases where the electrostatic interaction is repulsive. The effect of substitution is mainly reflected on changes in the molecular electrostatic potential of the bowl and, thus, in the electrostatic contribution to the interaction. Therefore, the variations in the stability of the complexes on substitution could be roughly predicted just considering the changes in the electrostatic interaction. However, other contributions also register changes mainly as a consequence of displacements on the position of the ion at the minimum, so the accurate prediction of the stability of this kind of complexes requires going further than the electrostatic approach.

Topics: Anions; Cations; Chlorides; Polycyclic Aromatic Hydrocarbons; Quantum Theory; Sodium; Static Electricity

Complexes formed by CN-substituted corannulene and sumanene with monovalent anions have been computationally studied to evaluate the effect of anion's nature and solvent upon the interaction. The results indicate that the most stable complex arrangement corresponds in all cases to the anion located by the center of the concave face of the bowl. All complexes are remarkably stable in the gas phase, with interaction energies ranging from -47 to -24 kcal/mol depending on the anion and the bowl considered. The order of stability for the different anion complexes in the gas phase is CO2H(-) > Cl(-) > Br(-) > NO3(-) ≫ ClO4(-) > BF4(-). Regarding the bowl employed, the intensity of the interaction is largest with the sumanene derivative substituted in the C-H aromatic groups. The weakest interactions are obtained with the sumanene derivative substituted in the CH2 groups, whereas complexes with the corannulene derivative give intermediate values. NO3(-) is oriented parallel to the bowl in the most stable complexes, whereas CO2H(-) prefers being oriented perpendicular to the bowl; ClO4(-) and BF4(-) arrange themselves with three bonds pointing to the bowl. These orientations are preferred on the basis of larger electrostatic and dispersion interactions. The preference of anions for the concave face of the bowl not only is mainly related to larger electrostatic interactions but also is because dispersion and induction are larger than in other arrangements considered. The presence of solvent modeled with a continuum model has a deep impact on the interaction energies already in solvents with low dielectric constant. All complexes remain stable, though energies in water hardly reach -7 kcal/mol. Br(-) complexes are the most stable in solvent, whereas CO2H(-) ones suffer a large penalty in solvent, becoming among the least stable complexes despite being the most stable in the gas phase.

Topics: Anions; Computer Simulation; Gases; Models, Chemical; Molecular Structure; Polycyclic Aromatic Hydrocarbons; Solvents; Water

Stacking interactions between substituted buckybowls (corannulene and sumanene) with fullerenes (C60 and C70) were studied at the B97-D2/TZVP level of theory. Corannulene and sumanene monomers were substituted with five and six Br, Cl, CH3, C2H, or CN units, respectively. A comprehensive study was conducted, analyzing the interaction of corannulenes and sumanenes with several faces of both fullerenes. According to our results, in all cases substitution gave rise to larger interaction energies if compared with those of unsubstituted buckybowls. The increase of dispersion seems to be the main source of the enhanced binding, so an excellent correlation between the increase of interaction energy and the increase of dispersion contribution takes place. One of the noteworthy phenomena that appears is the so-called CH···π interaction, which is responsible for the strong interaction of sumanene complexes (if compared with that of corannulene complexes). This interaction also causes the substitution with CH3 groups (in which one of the H atoms points directly to the π cloud of fullerene) to be the most favorable case. This fact can be easily visualized by noncovalent interaction plots.

Topics: Fullerenes; Kinetics; Molecular Structure; Polycyclic Aromatic Hydrocarbons; Quantum Theory; Receptors, Artificial; Thermodynamics

Buckybowls 7, 9, and 10 were prepared from benzo[k]fluoranthene 6 and fluoranthene 8 using straightforward procedures involving key palladium-catalyzed cyclization reactions. The structures of bowl-shaped molecules 7 and 10 were determined by using X-ray crystallographic methods. The observed p-orbital axis vector (POAV) angle of 7 was found to be 12.8°.

Topics: Catalysis; Crystallography, X-Ray; Cyclization; Models, Molecular; Molecular Structure; Palladium; Polycyclic Aromatic Hydrocarbons; Quantum Theory; Stereoisomerism