Chemical Kinetics (Reaction Mechanisms)

[jupiter_8917]

Can anyone please explain to me what is reaction mechanisms and intermediate? I have read my book many times, but I don't get it. Also, it would be great if you can me some examples about them. Thank you for your help!

 

[flemmyd]

reaction mechanism (or rxn mech): these are essentially the directions used, saying what electrons/bonds are interacting with what. you would say the a reactant leads to a product, but the point of the mech is knowing HOW you got there.
so you could say that product A was synthesized because the halogen acts as a great leaving group in the mechanism. by understanding the mecha, forming product B from slightly different reactants would makes sense because you have the same halogen leaving group on reactant B.

intermediate: if you want to go from california to new york, you will probably make stops along the way (grand canyon, etc). these midpoints are the intermediates towards your final destination.
like wise, you may do one with to a reaction(react with a metal at 80 C) to get product A. but you don't want product A. you want product D. so you do another reaction to product A to get product B (maybe react with an alcohol) and so on until you get to C and then to D.
in this case, A, B, and C are intermediates. there is no "scientific definition" about the intermediates. products A, B, and C are all fine molecules-- its just you don't want them. they may not have the properties you want, they may be unstable, whatever. they arent the molecules you're looking for.
ie. flour, eggs and milk are reactants. cake is the product. batter is an intermediate.

hope this helps. its been a while since orgo...

EDIT: kinetics is something fairly different. its about how molecules interact and how fast they go. one reaction might be really fast, another reaction might be really slow.
the relation is that you could say these two mechanisms would turn reactant A -> product A. but I would say mechanism A is unlikely as it involves some really slow parts (breaking carbon-carbon bonds maybe?) where as mechanism B is a super fast reaction (breaking a pi-bond?). yes, mechanism A would probably work, but you'd never see it because mechanism B just happens so much faster.

 

[Kracatoan]

http://www.chemguide.co.uk/mechmenu.html#top" explains it rather well.