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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: betterbesafehero on May 01, 2013, 01:08:54 PM

Title: Mechanism ?
Post by: betterbesafehero on May 01, 2013, 01:08:54 PM

Ph-CH₂-CH₂Br on treatment with C₂H₂OD/C₂H₅O^- gives Ph-CD=CH₂ as major product.

A picture mechanism would be great and easy to understand.

Hint: Follows E1cb mechanism...!

Title: Re: Mechanism ?
Post by: Dan on May 01, 2013, 05:57:54 PM

You must show you have attempted the question, this is a Forum Rule (http://www.chemicalforums.com/index.php?topic=65859.0).

Title: Re: Mechanism ?
Post by: betterbesafehero on May 01, 2013, 09:58:08 PM

^^^^Attempts for mechanism, It's hardly two or three steps, and maybe I don't even know the first step, so can't proceed further..! If you wanna see ruff work, I can show you that..!

Title: Re: Mechanism ?
Post by: orgopete on May 02, 2013, 04:15:15 PM

The deuterium exchange is simply telling you the deprotonation (and protonation) step is faster than the elimination. If that were not the case, no deuterium would be incorporated as every anion would result in elimination. That is not happening. Therefore, the reaction rate is first order in the benzylic anion, hence E1cb.

Although textbooks refer to concerted reactions, a closer look would show that reactions may have varying degrees of bond formation and breakage. A good example is Hofmann and Saytzev eliminations. Hofmann elimination are more E1cb-like and eliminate from the most acidic proton while Saytzev eliminations are more E1-like and result if loss of a proton from the most substituted carbon, or carbocation-like.

Title: Re: Mechanism ?
Post by: betterbesafehero on May 02, 2013, 04:22:22 PM

Fine..!!

I solved it later on myself. Thanks