How Dihalogens Catalyze Michael Addition Reactions. - NCBI - piectron?

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Discussion Overview

The discussion centers around the role of dihalogens in catalyzing Michael addition reactions, as presented in a paper published in a reputable journal. Participants explore the implications of a potential quantum level effect in the catalytic process and express concerns regarding typographical errors in peer-reviewed literature.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express uncertainty about the term 'piectron,' suggesting it may be a typographical error in the paper.
  • One participant clarifies that the term is a typo and should refer to ##\pi##-electron, based on the actual abstract from the journal.
  • There is a discussion about the assertion in the paper regarding a quantum level effect in the catalytic process of Michael addition reactions facilitated by halogens.
  • Some participants question the significance of the "Pauli repulsion" mentioned in the paper, suggesting it may be overstated and more of a marketing term.
  • One participant elaborates on the theoretical calculations presented in the paper, discussing the breakdown of energy calculations and the role of the Hartree-Fock exchange integral.
  • There is mention of the relationship between orbital overlap and activation energy in the context of frontier molecular orbital theory, with some skepticism about its advantages over simpler models.
  • One participant notes that the paper suggests halogens polarize the acceptor, decreasing electron density at the reaction center, which could enhance nucleophilic addition.
  • It is pointed out that the energy change in the reaction is dominated by the exchange integral rather than the electrostatic integral, explaining the varying effectiveness of different halogens as catalysts.
  • Concerns are raised about the implications of typographical errors in peer-reviewed articles, with a reminder that accepted articles may still contain such errors before final editing.

Areas of Agreement / Disagreement

Participants express a mix of curiosity and skepticism regarding the claims made in the paper. There is no consensus on the significance of the findings or the implications of typographical errors, indicating that multiple views remain on these topics.

Contextual Notes

Participants note that the paper discussed is an accepted article that has not yet undergone final editing, which may account for the typographical errors observed.

jim mcnamara
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TL;DR
Michael addition is found to be caused by Pauli exclusion. Question
How Dihalogens Catalyze Michael Addition Reactions. - NCBI

What Michael Addition is about: https://en.wikipedia.org/wiki/Michael_reaction

I do not know what the definition of 'piectron' is. In the abstract of the paper, I assume it is a misspell. Which makes me wonder?

I learned about Michael Addition in an Organic Chemistry class (loooong ago)- the use of halogens to catalyze many reactions. This paper is supposed to assert that there is a quantum level effect in how the catalytic molecule facilitates the reaction.

A really interesting idea. I do not know if it can be extended more generally.

I just get the heeby-jeebies when some mistakes like that in a peer reviewed journal. Makes you wonder what else got missed. And yes, I am the second worst typist here on PF. So I am well acquainted with stupid typographic errors.
 
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jim mcnamara said:
I do not know what the definition of 'piectron' is. In the abstract of the paper, I assume it is a misspell.
It's a typo on Pubmed. In the actual abstract at the Angewandte website, it's clearly ##\pi##-electron.
jim mcnamara said:
This paper is supposed to assert that there is a quantum level effect in how the catalytic molecule facilitates the reaction.
I suppose it's interesting, and Angewandte is a reputable journal. But it wasn't particularly surprising to me at first blush. I think the "Pauli repulsion" is more marketing than anything else. What they've done is theoretical calculations on the aza-Michael addition catalyzed by the halogens ##X_2##. They break their energy calculations into three main pieces, one of which is the Pauli repulsion. When I tried to follow the reference trail to find exactly how they calculated this, it took me down a rabbit hole that I got tired of. As far as I can tell, the Pauli repulsion they refer to is--at least in part--related to the Hartree-Fock exchange integral (the three main integrals that one calculates in HF theory to get energies are the Coulomb (electrostatic), the orbital overlap, and the exchange (Pauli) integrals).

The Michael addition is trotted out every once in a while as an example of frontier molecular orbital theory (NB--I'm not convinced this approach has advantages beyond a simple nucleophilic addition picture), where the activation energy is roughly inversely proportional to the overlap between the HOMO of one molecule and the LUMO of the other (the Diels-Alder reaction is the canonical example of this effect). The current paper asserts that the catalytic effect of the halogens on the Michael addition has less to do with the orbital overlap and more to do with reduced repulsion between specific filled orbitals on the reagent molecules.

The reason it doesn't surprise me much is that they're basically saying that the halogen polarizes the acceptor such that electron density at the reaction center decreases--exactly the kind of thing you'd expect to speed up a nucleophilic addition. I suppose the really interesting part of the paper is that the energy change here is dominated by the exchange integral, not the electrostatic integral. This also explains why iodine is a more effective catalyst than fluorine, as the electrostatic contribution is larger in fluorine than iodine, but the exchange contribution is larger in iodine.

Anyway, that's my takeaway from a first readthrough. Take it with a grain of salt.
 
jim mcnamara said:
I just get the heeby-jeebies when some mistakes like that in a peer reviewed journal. Makes you wonder what else got missed. And yes, I am the second worst typist here on PF. So I am well acquainted with stupid typographic errors.

Note that the paper is an accepted article, not the final article. Accepted articles have passed peer review but have not yet been copy edited by the journals. The final article will have undergone additional editing by the journal and authors to hopefully catch typos like that and other issues. The following disclaimer is present on the page for the article (https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201903196): "Accepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future."
 
Thanks. Saw the article on NIH archive. Still an interesting paper.