Based on the reaction: [compound]2+ + e- → [compound]+ where basically the starting compound gains an electron, I have found the following results (in Hartrees, with ZPE correction):
EE of [Compound]2+: -1301.17066
EE of TS: -1301.36606
EE of [Compound]+: -1301.36891
As you can see, the EE of the transition state is lower than that of the starting compound but still higher than the product. In terms of geometry, the TS makes sense. Is this possible? Do I have any consider anything in interpreting this result? Please advise.
Note: I've also got the same TS while I was doing QST2 calculation so I guess the geometry of the TS makes sense.
First, you must do a frequency calculation to verify that you indeed have ONLY one imaginary frequency for optimized TS and you have no imaginary frequency for optimized reactants.
Second, you must do an IRC calculation. One end of the IRC should be a structure that tends towards the reactants while the other end should give you a structure that tends towards products.
(If either of these structures look different from what you would expect, you may have identified the wrong TS or your reaction follows a mechanism different from the one you have hypothesized).
Finally, if your TS is right!, you must consider that when TS is energetically stable than reactants, TS formed from pre-complex instead of reactants. this pre-complex formed between reactants in an appropriate distance and also is energetically so stable than reactants.
Dear James,
Your reaction includes just an electron transfer (oxidation-reduction processes) and, such reactions do not include a TS!
You have just a thermodynamic equilibrium between, probably, two different conformers or something like this in two different oxidation states. Moreover, the mechanism of such an electron transfer should firstly be clarified.
Could you please attach optimized structure of reactant as well as located TS?
I am very suspicious of the nature of your TS!!
Regards,
Saeed
It was also forgotten to be indicated that there is a huge and highly non-logical energy difference between located TS and starting material, i.e. more than 122 Kcal/mol!!
On the other hand, energetically, your TS is highly resembles product. The difference in energy is ca. 2 kcal/mol.
Thus, do not doubt that what you have located as a TS is quite wrong!
Please, if possible, attached the structure which you call that TS.
Saeed
Hi All. Thank you for your comments.
TS has only one imaginary freq while products and reactants has no imaginary freq.
However, I believe I need to use Marcus Theory for my problem so I will be doing other type of calculation. Wish me luck. :)
The below links can help you, have a look:
1-https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Book%3A_Time_Dependent_Quantum_Mechanics_and_Spectroscopy_(Tokmakoff)/15%3A_Energy_and_Charge_Transfer/15.05%3A_Marcus_Theory_for_Electron_Transfer
2-https://www2.mpip-mainz.mpg.de/~andrienk/journal_club/marcus.pdf
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