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  •  » Why does (Z)-2-chlorobutenedioic acids eliminate faster then (E)?

#1 2010-12-05 09:03:31

orgopete
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Why does (Z)-2-chlorobutenedioic acids eliminate faster then (E)?

Both (E)- and (Z)-2-chlorobutenedioic acids dehydrocholorinate to give acetylene dicarboxlyic acid.

The Z acid reacts about 50 times faster than E acid. Explain

The rate differential is similar to the preference for antiperiplanar conformations in elimination reactions. The electrons of substitution reactions come from a "back-side" attack. A back-side attack in an elimination reaction is antiperiplanar. A back-side attack from an alkene elimination is from the (Z) alkene in this instance.

Syn-elimination reaction can also take place, but they are slower. See below:

         http://www.curvedarrow.com/chem/ZZ71720DD4.jpg

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