Geodesic Polyarenes by Flash Vacuum Pyrolysis

Reactivity and Selectivity of Bowl‐Shaped Polycyclic Aromatic Hydrocarbons: Relationship to C60

“…This is mainly due to the experimental difficulties associated with the synthesis of these molecules, which in many instances involves flash vacuum pyrolysis procedures and proceeds with low reaction yields. [6][7][8][9] Despite that, bowl-shaped PAHs share an important topological feature with fullerenes as both families of compounds are constituted by fused five-and six-membered carbon rings. As a result, we can find two different types of C-C bonds in these species: [6,6]-bonds, in which two six-membered rings are fused, and [5,6] bonds, corresponding to the ring junction between a five-and a six-membered ring.…”

“…[6][7][8][9] Despite that, bowl-shaped PAHs share an important topological feature with fullerenes as both families of compounds are constituted by fused five-and six-membered carbon rings. As a result, we can find two different types of C-C bonds in these species: [6,6]-bonds, in which two six-membered rings are fused, and [5,6] bonds, corresponding to the ring junction between a five-and a six-membered ring. Both C 60 and bowl-shaped fullerenes usually prefer [6,6]-bonds over [5,6]-bonds in their reactions, typically, addition and cycloaddition.…”

“…As a result, we can find two different types of C-C bonds in these species: [6,6]-bonds, in which two six-membered rings are fused, and [5,6] bonds, corresponding to the ring junction between a five-and a six-membered ring. Both C 60 and bowl-shaped fullerenes usually prefer [6,6]-bonds over [5,6]-bonds in their reactions, typically, addition and cycloaddition. [3,4] For C 60 , the physical factors behind this extraordinary selectivity were not completely understood until our recent study [10] using the Activation Strain Model (ASM) [11] in combination with quantitative molecular orbital (MO) theory and the Energy Decomposition Analysis (EDA) [12,13] method.…”

“…[3,4] For C 60 , the physical factors behind this extraordinary selectivity were not completely understood until our recent study [10] using the Activation Strain Model (ASM) [11] in combination with quantitative molecular orbital (MO) theory and the Energy Decomposition Analysis (EDA) [12,13] method. We found that, for the [4+2]-cycloaddition reaction between C 60 and cyclopentadiene, the major factor controlling the observed regioselectivity is the stronger interaction between the deformed reactants in the [6,6] reaction pathway along the entire reaction coordinate as a consequence of a more effective <HOMO(cyclopentadiene)|LUMO(fullerene)> molecular overlap involving the 3 [6,6]-pyracylenic C-C bond. This novel computational approach was also quite helpful to gain deeper insight into the differences of either reactivity or regioselectivity of higher fullerenes and endohedral fullerenes as compared to the parent C 60 .…”

“…The authors convincingly proved that there is good correlation between activation barrier and activation strain for these systems. The [5,6]-attacks have a high activation strain and consequently higher barriers. The activation strain was related to the need to pyramidalize the attacked C atoms when going from reactants to transition state.…”