Organic Chemistry Geometric Isomers Lab

[ohgeecsea]

Homework Statement

The experiment was changing dimethyl maleate into dimethyl fumerate, with the intent of being analogous to changing maleic acid into fumeric acid. In the experiment, we added 1 M Bromine in dimethylchlorine to our dimethyl fumerate, put the mixture in a hot water bath and next to a light for 10 minutes, then recrystallzied, filtered and got the melting point of the new substance.

I'm having trouble with one of the post-lab questions: Could you start with dimethyl fumerate, do the same reaction (and under experimental conditions where dimethyl maleate could be recovered) and get dimethyl maleate?

Homework Equations

I can't find the reaction anywhere online and I don't know how to type it out, but basically what happens is that Bromine with a free radical reacts with one of the double-bonded carbons to break the double bond and allow for rotation. Once rotation occurs, Bromine breaks free and a double bond is formed again. Thus producing the geometric isomer.

The Attempt at a Solution

I'm thinking it's NOT possible to do the reverse direction. Dimethyl fumerate is the trans-isomer, and is therefore more stable. In equilibrium with a single bond, most of the molecules are going to be in trans. Therefore I think if you redid the experiment in the reverse direction, you might get some yield but not a respectable amount.

I'm not really sure and don't have a whole lot of confidence in this answer, so I just wanted to bounce the idea off of someone else, see if it makes sense to them. Thanks :)

 

[chemisttree]

Sounds good to me.

 

[Blueshift5]

Your reasoning is correct. It is not possible to reverse the reaction and obtain dimethyl maleate from dimethyl fumerate. As you mentioned, dimethyl fumerate is the more stable geometric isomer and in equilibrium, most of the molecules will exist in this form. Reversing the reaction would require breaking the single bond and reforming the double bond, which would not be favorable under these conditions. Additionally, the experimental conditions used in the lab may not be sufficient to reverse the reaction and recover dimethyl maleate.