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Re: [Jmol-users] Jmol model kit bond lengths Robert Hanson Sun Feb 19 20:00:24 2012

The optimization is being done with the UFF force field. It's not a very
exacting field, and I'm not terribly surprised by this. Nothing really that
can be done from Jmol, I'm afraid.

On Sat, Feb 18, 2012 at 6:53 PM, <[EMAIL PROTECTED]> wrote:

> dear All
> For aromatic C-C bonds (eg in benzene) I would expect the bond lengths
> to be 140pm.  Jmol seems to think they should be 129pm.  This is what
> I am doing:
> 1. Create 6C membered ring with alternate single/double bonds using
> the model kit;
> 2. Choose 'Computation/Optimise structure' from right-click context menu;
> At this point the single bonds are 148pm and double bonds 134pm.
> 2. Select the C atoms 'select _C;
> 3. Execute command 'connect aromatic 1.5';
> 4. Execute command 'calculate aromatic'
> 5. Choose 'Computation/Optimise structure' from right-click context menu.
> This gives a six-membered ring with bond lengths all = 129pm.  This
> means the ring is smaller than it ought to be.  Are there some
> settings somewhere that I can change to get the correct bond lengths?
> Thanks
> Paul
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Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
phone: 507-786-3107

If nature does not answer first what we want,
it is better to take what answer we get.

-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
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