Silicon bond lengths

The rotational barrier in methylsilane (Table 3.4, entry 5) is significantly smaller than that in ethane (1.7 versus 2.88 kcal/mol). This reflects the decreased electron-electron rqjulsions in the eclipsed conformation resulting from the longer carbon-silicon bond length (1.87 A) compared to the carbon-carbon bond length (1.54 A) in ethane. 

Hyperconjugation should raise the bond order between the ipso and benzylic carbons, and lower the bond order between the benzylic carbon and the silicon atom. As the ipso-benzylic bond length decreases, the 13C-13C coupling constant should increase, and as the benzylic carbon-silicon bond length increases, the 13C-29Si coupling constant should... 

The first mercury(I) silyl complex [(Me3SiMe2Si)3Si]2Hg2 was prepared by the reaction of an excess of (Me3SiMe2Si)3SiH with (t-Bu)2Hg. The solid structure of the complex displays linear Si—Hg—Hg—Si fragment with regular metal-silicon bond lengths... 

Various photoreactions in which the silicon atom plays a less important role have been reported. The isolation of trans-1,2-diphenyl-4,4,5,5,6,6-hexamethyl-4,5,6-trisilacycloheptene (185), formed by irradiation of the corresponding cis-isomer (186), has been described the stability of this system is attributed to the long silicon-silicon bond lengths.Evidence for the intermediacy of a photochemically generated metastable trans-cycloalkene has also been reported in l,l,4,4-tetramethyl-l,4-disilacyclohept-2-ene. A novel [,2 + 2] photocycloaddition to give the bicycles (187) has been reported in the diallylsilanes (188) in the presence of 1,4,-dicyanonaphthalene. Intramolecular [ 2 + 2] photoaddition has also been observed in bis- and tetrakis-(4-vinyl-benzyl) silanes and their germane analogues,and the oxetanes (189) and (190) have been prepared by irradiation of 1,1-dimethyl-2,5-diphenylsilacyclopentadiene in the presence of benzophenone. 

In the same group (IVA) as carbon, silicon is very much like carbon in atomic structure. It forms silicon-silicon covalent bonds, but since silicon is over double the size of carbon, the silicon bond lengths are longer and weaker. It is like a bridge between two river banks. The bridge across a 4 meter (12 foot) wide stream will be much stronger and more stable than one across an 8 meter (28 foot) stream, when the middle is not supported. 

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