Re: ORGLIST: Challenge: To find Reaction with most bond forms/cleaves

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From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Mon Nov 30 1998 - 04:35:48 EST


Hello there,

A beautiful challenge. May I suggest for strarters the Claisen
rearrangement (ortho version) as an example involving 5 bonds? or did I
miss a point?

All the best,

Jacob Zabicky

>Can I set the following challenge?
>
>Over the years, I and my students have studied many types of reactions
>using Quantum chemistry modelling techniques. I was recently asked
>to write a lecture on "transition states", and started to wonder about
>examples of reactions classified by the total number of bonds actually
>formed or broken in what we will presume is a concerted (but not
>necessarily synchronous) transition state.
>
>Thus examples of 0, 1- 2- and 3- bond reactions are trivial to
>set down. 4-bond reactions are less common, and 5-bond reactions
>I suspect fairly scarce (I give two such here, namely peroxidation
>of an alkene by peracid; deoxygenation of the ozonlolysis intermediate
>by eg Ph3P). Can anyone think of any 6-bond and higher order reactions?
>I suspect some tandem radical reactions must be strong challengers,
>although here issues of whether the reactions are really concerted, or
>stepwise must come to the fore. If anyone knows of any calculations
>showing synchronicity in such tandem reactions, I would be most
>interested.
>
>Excluded from this challenge are what I would describe as examples
>involving concurrent lesser-bond examples, ie two concurrent
>Diels Alder additions to make a 4-bond reaction, which I think theory
>would almost certainly predict were stepwise (although see
>http://www.ch.ic.ac.uk/rzepa/RSC/P2/cr2/ )
>
>Dr Henry Rzepa, Dept. Chemistry, Imperial College, LONDON SW7 2AY;
>mailto:rzepa$##$ic.ac.uk; Tel (44) 171 594 5774; Fax: (44) 171 594 5804.
>URL: http://www.ch.ic.ac.uk/rzepa/
>If my digital email signature is invalid, download a new root at
>http://www.belsign.be/en/services/receive/install-ca.html
>__________________
>
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>List coordinator: Joao Aires de Sousa (jas$##$mail.fct.unl.pt)

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Prof. Jacob Zabicky Tel. 972-7-6461271/6461062/6472754
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