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标题: How to consider a theoretical study under phase transfer catalyst ? [打印本页]

作者
Author: Joao.T 时间: 2023-4-13 03:01
标题: How to consider a theoretical study under phase transfer catalyst ?
I want to study an organic reaction using quantum chemical methods (DFT) by the Gaussian program, the reaction take place between two reactifs under normal conditions, but the authors also have worked under phase transfer catalysis. where the phase transfer agent is bulky, and i don't know how to include in my calculations, so, i would like to know if i don't considered the phase transfer agent would affect significantly the calculations, i mean get a contradiction with experimental results.

作者
Author: wzkchem5 时间: 2023-4-13 04:12
The information you gave is not enough for us to answer your question. For example, exactly how bulky is the phase transfer agent? Is the phase transfer agent chiral? Does the phase transfer agent interact with the solute via interactions other than electrostatic attraction and vdW interaction?

作者
Author: Joao.T 时间: 2023-4-13 05:39

wzkchem5 发表于 2023-4-13 04:12
The information you gave is not enough for us to answer your question. For example, exactly how bulk ...

The phase transfer agent used is the Benzyltriethylammonium chloride (catalytic amount), sodium hydroxid is also present, and CHCl3 as a solvent, and the main reactif, an alkene, that is all the reactifs mentioned by the authors in the experimental procedure.

作者
Author: wzkchem5 时间: 2023-4-13 06:22

Joao.T 发表于 2023-4-12 22:39
The phase transfer agent used is the Benzyltriethylammonium chloride (catalytic amount), sodium hy ...

OK I see. If I understand correctly, the phase transfer agent [BnNEt3]Cl and NaOH serve only to generate dichlorocarbene, right? Since this chemistry is extremely well-known, for most intents and purposes it is not necessary to study this step, and you can start your calculation from the reaction of CCl2 with your molecule.
If, for example, you want to know how much CCl2 was lost due to its reaction with excess [BnNEt3]OH, or your alkene is an anion that can also pair with [BnNEt3]+, then it may be necessary to include the [BnNEt3] cation in your calculations. This can be done by simply putting the [BnNEt3] cation close to the anion that you want to study, and (very important!) do a configurational search to deduce the optimal position of the [BnNEt3] cation. Putting [BnNEt3]+ at a random place near the anion without performing a configurational search is generally not acceptable, even if the structure is optimized and there is no imaginary frequency. Configurational searches cannot be done by Gaussian alone, but can be done with the help of external programs like CREST and Molclus, which are free and easy to learn. Moreover, it is also important to verify that the non-covalent complexation of [BnNEt3]+ with your anion is indeed thermodynamically favored (from Gibbs free energy calculations), since the complexation is enthalpically favored but entropically disfavored. If not, then you should not include [BnNEt3]+ in the calculation of that species.

作者
Author: Joao.T 时间: 2023-4-13 07:09

wzkchem5 发表于 2023-4-13 06:22
OK I see. If I understand correctly, the phase transfer agent Cl and NaOH serve only to generate d ...

Thank you very much, i'm most grateful.

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