Chains, Rings, Cages, and Clusters

If there is a single feature of carbon which makes possible a unique branch of chemistry devoted to a single element. it is its propensity to form extensive stable chains. This phenomenon is not common in the remainder of the periodic table. 

In fact both reactions are thermodynamically favored to proceed to the right. The important difference, not apparent in the stoichiometric equations, is the energy of activation which causes the paraffins to be kinetically inert in contrast to the reactive silanes.  

Oxygen forms no chains longer than three atoms, and besides the bmiliar ozone. O,. and its anion. Oj, few compounds are known all of them are bisfperfluoroalkyl) trioxides such as F,COOOCF,. 

Alloiropes of both sulfur and selenium are known in which helical chains of great length are present. While the sulfur chains are unstable with respect to cyclic S. the chain form for. selenium is most stable. Red phosphorus is polymeric and is thought to involve chains of pyramidal phos )horus atoms. 

The extensive chemistry of metal-metal bonds is sufficienlly iraeresting to warrant separate treatment (page 807). 

Choins If there is a single feature of carbon which makes possible a unique branch of 

Further complications with silanes arise from lack of convenient syntheses and difficulties in separation. Nevertheless, compounds from n - I to n = 8 have been isolated, including both straight-chain and branched-chain compounds. We should not judge silicon s tendency to catenate by looking at these hydrides, however, since a much dilTcrem result is obtained when substituents other than hydrogen are present.7 Factors other than inherent Si—Si bond strength must be involved because it is possible to isolate a large number of polysilane polymers 11 

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