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Explain fullerenes. |
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Answer» Solution :Fullerenes are made by the heating of graphite in an electric arc in the presence of inert gases such as helium or argon. The sooty material formed by condensation of vapourised `C^n` small molecules consists of mainly `C_60` with smaller quantity of `C_70` and TRACES of fullerenes consisting of even number of carbon atoms upto 350 or above. Fullerenes are the only pure FORM of carbon because they have smooth structure without having .dangling. bonds. Fullerenes are cage like molecules. `C_60` molecule has a shape like soccer ball and called Buckminsterfullerene.  It contains twenty six-membered rings and twelve five-membered rings. A six-membered ring is fused with six or five membered rings but a five membered ring can only fused with six membered rings. All the carbon atoms are equal and they undergo `sp^2` hybridisation. Each carbon atom forms three sigma bonds with other three carbon atoms. The remaining electron at each carbon is delocalised in molecular orbitals, which in turn GIVE aromatic CHARACTER to molecule. This ball shaped molecule has 60 vertices and each one is occupied by one carbon atom and it also contains both single and double bonds with C-C distances of 143.5 pm and 138.3 pm respectively. Spherical fullerenes are also called bucky balls in short It is very important to know that graphite is thermodynamically most stable allotrope of carbon and therefore, `Delta_fH^ɵ` of graphite is taken as zero. `DeltafH^ɵ` values of diamond and fullerene, `C_60` are 1.90 and 38.1 kJ `"mol"^(-1)` respectively. Other forms of elemental carbon like carbon black, COKE and charcoal are all impure forms of graphite or fullerenes. Carbon black is obtained by burning hydro carbons in a limited supply of air. Charcoal and coke are obtained by heating wood or coal respectively. |
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