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Re: catalysis, negative energy activation in MP2 calculation

sanya
sanya@photonics.ru


Look at this picture. You can see that the catalytic reaction system actually passes through several transition states and intermediate minima. For each elementary step (from one local minimum to the next one), the real activation energy of the system including reagent X + reagent Y + catalyst C is positive.

The general mechanism of any catalytic reaction is the following:

X + Y + C -> XYC* (transition state 1) -> XYC1 (intermediate 1) -> XYC** (transition state 2) -> XYC2 (intermediate 2) -> ... -> ZC (catalyst--product intermediate) -> ZC* -> Z + C

That is, the real mechanism may be very complex, and each step should be treated separately. Of course, you should take X + Y + C as reactants, XYC* as a transition state, and XYC1 as a first product. Next, take XYC1 as a reactant, XYC** as a transition state, and XYC2 (or Z + C if no more steps is expected). And so on. Good luck!

On Mon Feb 22 '10 2:44pm, Ronald Conol wrote
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>dear reader,

>Can we include the energy of the catalyst in the Product and reactant  when dealing with catalytic reaction  to calculate the energy of activation? because i am just confused about the nature of  a catalyst that it does not participate in the chemical reaction.. and if i wont include the energy of the catalyst. the difference between the energy(product,TS and reactant) from free to catalyze reaction is so far ,say -323.88XX hartree/particle.

>here is the reaction that I've studied:

> 1-methylcyclopentadiene + acrylonitrile ------BF3----> 1-methylbi[2,2,1]cyclohexene.

>where BF3 acts as my catalyst..
>
>
>also.. is it possible to get a negative energy of activation ?. because when i employed HF calculation the Ea is quiet reasonable.. but when i refined my result using MP2 calculation i got negative energy of activation (using catalyst). and the result is the almost the same when i used the PCGAMESS and FIREFLY. 6-31G**(d,p) was the basis set that i have used in both HF and MP2 calculation. i have attached my output file so as to prove that i have located the transition state with catalyst.
>
>


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