Alkenes by Dehydration of AlcoholsTable of contentsNo headersKim Quach says:
Good job! This is a very descriptive and simple explanation. :)
Just a few points to make your module a little clearer. You might want to include a link to E1 and E2. You do a nice job explaining the overall mechanisms but it would help those who want more info on elimination. You can also show backside attack for E2 in your reaction diagram. Under tertiary alcohols, you say "thermodynamically most stable alkene." Is trans considered as thermodynamically favorable? Or is the most substituted alkene considered thermodynamic? (Explain what your mean by thermodynamic) You might want to explain what the kinectic product is too to give a complete description of what products are produced. You can also explain the products produced with an energy/rxn coordinate graph/diagram. Posted 13:48, 3 Mar 2009
Chin Kan says:
This is excellent work!! It gives clear explainations of everything, even hydride shifts and alkyl shifts. The E1 and E2 mechanisms are very easy to understand!!!
Here are some suggestions, maybe you can explain why trans is less favourable than cis products in dehydration of tertiary alcohol, maybe due to steric hindrance and why are tertiary alkene more stable? maybe due to induction and hyperconjugation stabilization? But overall this is an excellent job!!! ^_^ edited 10:41, 7 Mar 2009 Posted 10:37, 7 Mar 2009
Satish Balasubramanian? says:
Great module! It entails a lot of description and explanations. A suggestion I have for you is to explain why primary alcohols favor E1, and secondary favor etc.. You should go into the idea behind hyperconjugation, and the stabilizing effect it has on carbocation intermediates. This would allow the reader to grasp the concept better than merely memorizing. Also, you may want to elaborate on the product section in which you state that trans is a more favorable product. Why is this the case, and are there any exceptions? These are a few suggestions, however your page clearly explains the overall topic in great detail. Good job! |
the page is http://chemwiki.ucdavis.edu/Organic_Chemistry/Hydrocarbons/Alkenes/Alkenes_by_Dehydration_of_Alcohols
the errors pertain to the diagrams showing the dehydration of tertiary alcohols. the diagrams explaining this mechanism shows a secondary alcohol being dehydrated.
Also a tri-substituted alkene is shown as the minor product while the major product is show to be a trans alkene
I believe the tri-substituted alkene is the most stable product (lower energy). the two di-substituted alkenes should be the minor products, with the cis isomer being the least favored (highest energy).
I have never edited a wiki site before, so I thought the best thing to do would be bring this to you attention.
The comment by zpriest is also correct, a primary alcohol wouldn't undergo an SN1 dehydration - better to illustrate rearrangements starting with 2o or 3o alcohols. This is true both in the problem and in the main text example. When showing the E2 dehydration of a primary alcohol, it would be good to mention that there is competition with SN2 reactions to form ethers.
Chin Kan just mixed up terms, the trans alkene is favored over the cis (sounds like this is what he/she meant, but just made a typo)
Hope this helps! I think the writer did a very good job, it's a tough thing to explain because so many different things are going on. I think the key is to pick the right examples so that each variation can be explained in turn.