Catenate compounds

The ability of C to catenate (i.e. to form bonds to itself in compounds) is nowhere better illustrated than in the compounds it forms with H. Hydrocarbons occur in great variety in petroleum deposits and elsewhere, and form various homologous series in which the C atoms are linked into chains, branched chains and rings. The study of these compounds and their derivatives forms the subject of organic chemistry and is fully discussed in the many textbooks and treatises on that subject. The matter is further considered on p. 374 in relation to the much smaller ability of other Group 14 elements to form such catenated compounds. Methane, CH4, is the archetype of tetrahedral coordination in molecular compounds some of its properties are listed in Table 8.4 where they are compared with those of the... 

A laboratory preparation of the simplest of these catenation compounds. two interlocking rings, has been carried out at AT T Bell Laboratories. They started wilh the dimethyl ester of a 34-carbon paraffinic dicarboxylic acid, CH ,OOC-(CH )j2-COOCHi, which was reacted in a suspension of metallic sodium in xylene with acelic acid to condense the terminal ester groups to form an aceloin ring compound. 

Separation and identification of this catenation compound was effected by chromatography and infrared spectroscopy, the latter being the reason why the hydrocarbon portion of ihe catenation compound was deuterated. 

For a given class of compounds, members with C—Si and C—Ge bonds have higher thermal stability and lower reactivity than those with bonds to Sn and Pb. In catenated compounds similarly, Si—Si and Ge—Ge bonds are more stable and less reactive than Sn—Sn and Pb—Pb bonds for example, Si2Me6 is very stable, but Pb2Me6 blackens in air and decomposes rapidly in CCI4, although it is fairly stable in benzene. 

The formation of the Si-Si bond occupies a special position in organosilicon chemistry. Silicon is one of the few elements, which can form stable catenated compounds. Besides high-molecular weight polysilanes, oligomeric polysilanes are a very important class of compounds that are related to silylenes,... 

Tetramethyldiarsanse (CH3)2AsAs(CH3)2 is one of first organometallic compounds to be made. It s a catenated compound based on As-As bonding. 

These reactions were promptly extended to not only other polysilanes having more than two contiguous silicon atoms but also to catenated compounds of other Group IVB elements. 

As in carbon chemistry, catenation is an important feature in silicon and germanium chemistry. However, unlike carbon catenated compounds, main chain, and these... 

At the interface of main group and transition metal chemistry, Frenking, Fischer et al. describe recent developments in which monovalent gallium species can serve as ligands for transition metals, thereby affording a variety of compounds that feature M-Ga bonds. Furthermore, many of these compounds with M-Ga bonds can be converted into compounds that feature M-Zn bonds. Also, with respect to main group chemistry. Hill discusses catenated compounds of Group 13-15 elements, which feature chains of M-M bonds. 

The effect of substituents on the thermal stability of catenated derivatives is worth noting stability increases in the sequence halide < organo. Significantly, the substituents which stabilize catenated compounds are not those which form the strongest bonds to the Group IV elements, but those which release electrons most readily. It is likely that the M—M bond energy in a derivative pC(8-)]3M(8- -)-M(8-t-)pC(8-)]3 is sensitive to the size of the positive charge 8- - on M, and if, as seems likely in many cases, fission of the M—M bond is a key step in their decomposition, the stability sequence is readily understood. 

If one ignores catenated compounds (those in which atoms of the element in question are bound to each other), the typical elements tend to form oxidation numbers that differ by multiples of two. Thus, sulfur exists in oxidation numbers -2, 0, +2, +4 and +6 as usual, the highest oxidation number is equal to the number of outer electrons. The so-called inert pair effect is most clearly seen among the elements of Periods 4, 5 and 6 in Groups III, IV and V (Figure 13.9) from Period 3 to Period 6, the lower oxidation number, which is two less than the number of outer electrons, tends to increase in stability relative to the higher oxidation number. 

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