Group 14 elements Tetramethyl derivatives

Fig. 13.1. Periodic variation of bond distances in subvalent chlorides, ECI2, Lewis-valent chlorides, ECI4, and tetramethyl derivatives, E(CH3)4, of the Group 14 elements.

Table 13. Gaseous tetrahydrogen and tetramethyl derivatives of the Group 14 elements bond distances and mean bond energies.

The heavier elements of the group, S, Se and Te all form tetralluorides, EF4 and hexafluorides, EF6- If the central atom in these compounds form Lewis electron pair bonds to all the ligating fluorine atoms, it must accommodate five or six electron pairs in the valence shell, and we refer to the atoms as hypervalent. Sulfur forms no further homoleptic hypervalent derivatives. Selenium forms a solid tetrachloride, but as mentioned in the last paragraph, it decomposes on evaporation. Tellurium forms a solid tetrachloride, which may be evaporated without decomposition, as well as tetraphenyl-, tetramethyl- and hexamethyl- derivatives. 

Most HALS are derivatives of 2,2,6,6 tetramethyl piperidines. Figure 3.8 shows the structure element typical of HALS, the piperidine group, and a simplified scheme of the stabilization reaction. The working principle of these stabilizers differs from those mentioned earlier in that here we see a stabilization cycle in which the stabilizer is regenerated [510],... 

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