|
Fullerene chemistry is a field of organic chemistry devoted to the chemical properties of fullerenes. Research in this field is driven by the need to functionalize fullerenes and tune their properties. For example, fullerene is notoriously insoluble and adding a suitable group can enhance solubility.〔 By adding a polymerizable group, a fullerene polymer can be obtained. Functionalized fullerenes are divided into two classes: exohedral fullerenes with substituents outside the cage and endohedral fullerenes with trapped molecules inside the cage. ==Chemical properties of fullerenes == Fullerene or C60 is soccer-ball-shaped or ''Ih'' with 12 pentagons and 20 hexagons. According to Euler's theorem these 12 pentagons are required for closure of the carbon network consisting of ''n'' hexagons and C60 is the first stable fullerene because it is the smallest possible to obey this rule. In this structure none of the pentagons make contact with each other. Both C60 and its relative C70 obey this so-called isolated pentagon rule (IPR). The next homologue C84 has 24 IPR isomers of which several are isolated and another 51,568 non-IPR isomers. Non-IPR fullerenes have thus far only been isolated as endohedral fullerenes such as Tb3N@C84 with two fused pentagons at the apex of an egg-shaped cage. or as fullerenes with exohedral stabilization such as C50Cl10 and reportedly C60H8. Because of the molecule's spherical shape the carbon atoms are highly pyramidalized, which has far-reaching consequences for reactivity. It is estimated that strain energy constitutes 80% of the heat of formation. The conjugated carbon atoms respond to deviation from planarity by orbital rehybridization of the sp² orbitals and pi orbitals to a sp2.27 orbital with a gain in p-character. The p lobes extend further outside the surface than they do into the interior of the sphere and this is one of the reasons a fullerene is electronegative. The other reason is that the empty low-lying pi * orbitals also have a high s character. The double bonds in fullerene are not all the same. Two groups can be identified: 30 so-called () double bonds connect two hexagons and 60 () bonds connect a hexagon and a pentagon. Of the two the () bonds are shorter with more double-bond character and therefore a hexagon is often represented as a cyclohexatriene and a pentagon as a pentalene or ()radialene. In other words, although the carbon atoms in fullerene are all conjugated the superstructure is not a super aromatic compound. The X-ray diffraction bond length values are 139.1 pm for the () bond and 145.5 pm for the () bond. C60 fullerene has 60 pi electrons but a closed shell configuration requires 72 electrons. The fullerene is able to acquire the missing electrons by reaction with potassium to form first the salt and then the In this compound the bond length alternation observed in the parent molecule has vanished. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fullerene chemistry」の詳細全文を読む スポンサード リンク
|