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16.6 Conjugated Dienes

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    Dienes can adopt two possible conformations through rotation about the single bond joining the two double bonds: the s-cis and the s-trans conformations.

    The energy barrier to isomerization is normally low, and the s-trans conformer is often more stable than the s-cis conformer.

    Naming Dienes

    First identify the longest chain containing both carbons with double bonds in the compound. Then give the lowest possible number for the location of the carbons with double bonds and any other functional groups present (remember when naming alkenes that some groups take priority such as alcohols). Do not forget stereochemistry or any other orientation of the double bond such as (E/Z,cis or trans).



    Different conformations of Conjugated Dienes

    There are two different conformations of conjugated dienes which are s-cis and s-trans conformations. s-cis is when the double bonds are cis in reference to the single bond and s-trans is when the two double bonds are trans in reference to the single bond. The cis conformation is less stable due to the steric interation of hydrogens on carbon. One important use of the cis conformation of a conjugated diene is that it is used diels-alder cycloaddition reactions. Even though the trans conformation is more stable the cis conformation is used because of the molecule's ability to interconvert and rotate about the single bond.


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