Abstract
The lower molecular weight hydrocarbons that can be mapped on the buckminsterfullerene (C60) structure are commonly known as "buckybowls" or "geodesic polyarenes" and have the distinctive characteristics of preserving the curvature and aromaticity of fullerene. These bowl-shaped structures are expected to be quite rigid. Nevertheless, the smaller members of the family, in spite of its substantial curvature are surprisingly flexible undergoing rapid bowl-to-bowl inversion in solution as evidenced by the dynamic NMR behavior of C20H10 (corannulene) and several of its derivatives. With the aim of gaining understanding in the bowl-to-bowl inversion, the present theoretical study has explored the effect that substitution of some of the hydrogen atoms of corannulene has on this process. The model systems studied have the formula C20H10-nRn with R = -Cl, -Br, -C≡CH, -CH3 and n = 0, 2, 4, 5, 6, 8, and 10. It is observed that the bowl depth is reduced only by high substitution levels or by a substitution pattern that conduces to important peri interactions. Full substitution with bulky groups causes a pronounced repulsion and the deformation of the transition structure for bowl inversion that otherwise is planar. The activation barrier for the inversion – bowl depth data fit an empirical quartic/quadratic function used previously in similar systems but the coefficients of the fitting don\'t follow the predicted substituent independency.
Highlights
Since the discovery of fullerenes contemporary chemists have been stimulated to investigate properties of this promising class of compounds.[1]
Equivalent tendencies with only small numerical discrepancies were observed between the results calculated by different DFT methods mainly when combined with the TZVP basis set
The repulsion among the peripheral groups reduces the depth of the corannulene core as well as the value of the energy barrier related to the bowl-to-bowl inversion process
Summary
Since the discovery of fullerenes contemporary chemists have been stimulated to investigate properties of this promising class of compounds.[1]. As another parameter for describing the geometry of the bowl the mean value of the hub-hub-flank dihedral angles (D) were calculated as well. Frequency calculations were used for characterizing the transition states and inversion barriers (∆Einv) were computed as the electronic energy difference between the transition state and its corresponding minima
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