Henry, so you are saying you think something is wrong with that pathway. From what I can see, there are two possible pathways from the chair -- one with a twist to the "left"; one with a twist to the "right."  The enatiomeric twist is not depicted. (Although I think you could invert the configuration of all models and see it!) So from the get-go, symmetry is broken. Nothing wrong with that.... The entire sequence is chiral!


On Wed, Feb 23, 2011 at 1:29 PM, Rzepa, Henry <h.rzepa@imperial.ac.uk> wrote:
>Hens! Good to hear from you. I hope you don't mind my co-opting your model -- reminds me that I need to put a link to WeTChe there.
>I'd love a little discusson of this, because I'd like to get this out there. My understanding is that both are "correct" -- the boat transition state is lower than the twist chair (though I don't see exactly why)

Because the angles are opened up beyond  109 in the half chair

>, and so statistically the molecule will find itself more often in a boat than a twist chair anyway, I think the "synthetic organic chemist"  should realize that what is
>shown is not a potential surface, but one degree of freedom singled out.

Surely a molecular dynamics trajectory is more accurate, since a degree of freedom can only be harmonic and you cannot have harmonic modes connecting the entire surface? The MD trajectory seems to show a boat transition state being involved at the half way point, not a twist boat minimum?

My concern is that a single degree of freedom singled out does not marry with group theory!


+44 (020) 7594 5774 (Voice); Blog: http://www.ch.ic.ac.uk/rzepa/blog/
 Dept. Chemistry, Imperial College London, SW7  2AZ, UK.

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