[organoman]

Hi all,
In the field of research we have been using the term thermodynamically controlled reactions and kinetically controlled reactions. However I don't know the exact difference between them. I have some vague idea about the two but not a very clear one. Can somebody tell me what are the exact differences between these two terms and how is a reaction said to be thermodynamically controlled and kinetically controlled one.
Can somebody suggest for some link to elaborate on this.
Regards,
ORG

[movies]

A kinetically controlled reaction will give predominantly the product that forms fastest (i.e., the one with a lower transition state energy).  A reaction under thermodynamic control will give mostly the lower energy final product, even if the transition state energy is somewhat higher.

Usually kinetically controlled reactions are carried out at low temperature to prevent reaction through a (relatively) high energy transition state and exclusively favor the low energy transition state while preventing reverse reaction.  Thermodynamically controlled reactions are usually at higher temperature and for longer time periods to allow everything to equillibrate to the lowest energy state.

[Custos]

That's right. I like to think about it visually (see attached). The reaction pathway leading to the kinetic product is "easier" (lower energy transition state hump) but the product is less stable (higher in energy) than the product of the thermodynamic pathway. If you carry out the reaction at high enough temperature to allow either pathway (remembering that the reaction pathways are reversible) all of the product will end up at the lowest energy - the thermodynamic product. If you give the reaction just enough energy to get over the red hump, but not enough to get over the blue hump, the product will all be the kinetic product.

[organoman]

Thank you Custos & Movies for this very clear idea.
Though I am still looking for some deeper information on this. May be some nice link can help.
regards,
ORG

[movies]

I don't understand what more you are looking to find out.  Could you explain what exactly you are looking for?

[organoman]

Dear Movies,
I want some more examples with description so that I have some experience with these kind of reactions.
While conducting a reaction everytime I don't get thermodynamic and kinetic data of all possible side reactions and impurities. I guess having gone through with some such reaction on paper I may able to do better if I come across such reaction (Though I guess almost every product has more than one possible product in Organic reactions).
Also with having some more knowledge on this subject I can find a link between thermodynamic/kinetic properties and many thumb rules such as Sayzef and Markownikoves in order to decide the predominance of one isomer or product over other. Even this can be linked with steriochemistry of the end product formed in different condition.
Regards,
ORG

[AWK]

http://eprints.ru.ac.za/252/03/PUBLICATIONS/JCHEMED62.pdf
http://careerchem.com/COURSES/3021/Kinetic-Thermodynamic-Control.pdf
http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Reactions/ReactionProfiles.html

[movies]

Those links are great!  Thanks AWK.

I'm not so good at following all the math, but the energy diagrams make a lot of sense to me as visual aids.  Take a look at the links and post if you have any other questions.

[organoman]

Thanks AWK,
That's exactly what I wanted.
Thanks a lot.
regards,
ORG