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saeed_E

Member

Registered: 2019-12-21

Posts: 244

Comparison two reactions. Which one is reasonable?

Dear Tian,

If possible, please let me ask you a question.

As you know much better than me, Professor Bickelhaupt and through activation/strain model (ASM) emphasizes to study reactions for comparison purpose along the whole reaction path. His justification is quite reasonable and understandable why one should consider the whole reaction. On the other hand, he performs EDA at a consistent geometry point. I think this approach should be considered for any given reaction.
Please let me explain you my mean by a simple example. Suppose that F-Cl interacts with C=O. This interaction can competitively take place from carbon and oxygen side of C=O leading to FCl...C=O or FCl...O=C halogen bonds. The goal is explore why one complex is preferred over other one. Considering Bickelhaupt point of view and this fact that optimized complexes are located at quite different Cl...C and Cl...O separation, we are not allowed to only consider optimized complexes and perform an EDA to find which factor acts as predominant one. Indeed, we have to initially perform a relaxed scan task over both separations mentioned and then draw the PES and find the consistent geometry point along the X-axis. Then, taking structure of both complexes at consistent geometry point, we can do EDA to find the dominant player. Indeed, we cannot only focus on the optimized complexes along a reaction.
Thus, it seems this approach should be considered to perform a reasonable comparison for any given set of reactions such as Diels-Alder, 1,3-dipolar, non-covalent interactions and so on.

Could you please let me your highly valuable opinion.

Sincerely,
Saeed

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: Comparison two reactions. Which one is reasonable?

Dear Saeed,

Performing EDA at respective minimum geometry is more meaningful. The minimum separation distance itself is also inherently related to electronic structure and interaction. If consistent separation is used for analysis, the interaction distance will be elongated or compressed, which brings artificial effect.

Tian

saeed_E

Member

Registered: 2019-12-21

Posts: 244

Re: Comparison two reactions. Which one is reasonable?

Dear Tian,

Many thanks for your so informative and nice comments, my nice friend.
If so, why in the ASM analysis, taking only TSs structures and perform a single analysis over TSs (instead of whole reaction coordinate) can lead to a completely wrong conclusion?
Sincerely,
Saeed

Last edited by saeed_E (2024-06-07 15:15:09)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: Comparison two reactions. Which one is reasonable?

Dear Saeed,

The two cases are not directly comparable, the situations are different.

Tian

saeed_E

Member

Registered: 2019-12-21

Posts: 244

Re: Comparison two reactions. Which one is reasonable?

Dear Tian,
Please excuse me but I did not get your mean. Could you please make your mean more evident? Indeed, please let me know what is the difference between comparison of two halogen-bonded (e.g. F-Cl...C=O)and hydrogen-bonded (H2O...HCl) complexes at their complete optimized geometry, and between two regioisomeric TSs in a cycloaddition reaction.

Sincerely,
Saeed

Last edited by saeed_E (2024-06-07 23:22:02)