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

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From: Rzepa, Henry (h.rzepa$##$ic.ac.uk)
Date: Mon Nov 30 1998 - 06:01:40 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


I think I was not specific enough in my definition. To simplify the
matter, I wished to regard only changes in bond order zero => 1 (are there
any where a zero bond goes directly to a double bond? Metallocarbenes?)
or vice versa. Of course, if one allows bond order changes m => m',
where both m and m' are non zero, then very large possibilities suggest
themselves, ie the double bond isomerism of an [n] annulene would
immediately result in a n-th order reaction.

>From a theoretical point of view, the most interesting reactions
(ie are they synchronous, are they concerted, are they concurrent)
are where bonds are formed where none existed before, and of
course the reverse. This is all to do with electron correlation,
spin coupling and all manner of heavy theoretical stuff. Anyway,
according to this criterion, alkene + peracid is 5 bonds (2 C-O formed,
one O-O cleaved, one O-H formed and one O-H broken). Most
QM theories agree that these all form/break in concert, although not
synchronously (at least in the gas phase; perhaps solvation
reduces the concert). The challenge is to find any 6-bond and 7-bond
reactions according to these criteria. For example, is the peroxidation
of a cyclopropane to a 4-ring ether a known reaction? If so, it would
be an example of a 6-bond reaction.

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/
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