Hello, I\'m trying to figure out what is the best mechanism for theIsomerization

Question

Hello,

I'm trying to figure out what is the best mechanism for theIsomerization of Maleic Acid to Fumaric Acid here:-

http://img19.imageshack.us/img19/1209/mechanismandspartanvalup.jpg

http://img19.imageshack.us/img19/9227/mechanismandspartanvaluu.jpg

http://img19.imageshack.us/img19/9707/mechanismandspartanvaluj.jpg

Also, I'm trying to understand How do the results obtained in thetest using hydrobromic acid support the correct mechanism?

2- why does not sulfuric acid induce the isomerization?

3- why is the reaction of 1 g of maleic acid with 1.5 ml of H2O and2 ml of conc. HBr is going slowly? What I'm gonna get if I usedHI ??

Thank you sooooo much for your help

Explanation / Answer

We Know that :      The Isomerization of MaleicAcid to Fumaric Acid is Carried through RadicalMechanism.        For the given mechanismMechanism 3 is best Suited for the isomerization of Cisisomer to Trans - isomer .       The Transition shouldposses lower the energy which means more will be the stability somore favoured the product       Formation.      We generally cannot use Su;phuricacid for the isomerization as sulphuric acid cause the dehydrationof Maleic acid         to give Maleicanhydride.       The Reaction goes slowly withConc. HBr as it is not a very good leaving group so theReaction goes slowly if we      use HI the Rate of the reactionincreases as I is better leaving group.

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