Ethane, C2H6, and Diborane

Q Why do compounds of formulae XH2CCH2X not have cis-trcms isomers  

A The C-C bond is a a bond and is cylindrically symmetric. There is free rotation about such a bond, so there is only one form of the XH2CCH2X compounds. 

The hydrogen Is orbitals may be regarded in their usual group forms  

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Molecules of formula A2H5 include ethane C2H6 and diborane B2H6. Important structures of ethane are the staggered and eclipsed conformations, 10.1 and 10.2, respectively. Diborane adopts the bridged structure 10.3, as noted in Section 9.3. The... 

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