Subject: DFT calculations of NMR shifts in norbornadiene

From: "Dr. Dave Winkler" <[email-masked]>
Date: Mon, 5 Feb 2001 12:58:42 +1100

Dear Netters,

I hope someone can provide a simple answer to a frustrating problem.

I've run DFT TZVP/bp calculation on cubane using DGauss and got excellent
agreement between IGLO/LORG values and experiment or 13C shifts.  I'm
trying to do the same with norbornadiene  (same basis set) and get crazy
values compared with experiment, particularly for the proton shifts.  The
sp2 and sp3 carbon 13C shifts seemed to be reversed compared with
experiment.  The geometries are optimized at DFT TZVP/bp too.  Gaussian HF
calculations get much closer to experiment.

Cheers,

Dave

Dr. David A. Winkler                    Email: [email-masked]
Senior Principal Research Scientist     Voice: 61-3-9545-2477
CSIRO Molecular Science			Fax:   61-3-9545-2446
Private Bag 10,Clayton South MDC 3169   http://www.csiro.au
Australia 	        		http://www.molsci.csiro.au

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From: "Bruce. Tattershall" <[email-masked]>
Date: Mon, 5 Feb 2001 09:25:51 +0000 (GMT)

I have been looking at GIAO calculations of phosphorus shifts in phosphorus
sulfides which have norbornane structures, and have had similar experiences.
One gets something like the right differences between isotropic shieldings
at quite a low RHF level, even 3-21g* for both geometry and GIAO.  By doing
a least squares fit of shieldings to experimental shifts, i.e. calculating
an effective shielding for the standard and hence absorbing a lot of 
systematic error, one can get useful information to allow one to 
distinguish between isomers, invertomers or rotamers, which is generally what
I want to do as a synthetic chemist.

Increasing the level of the calculations frequently helps little.  Relative
energies become more realistic as expected, e.g. reflecting observed 
isomer ratios, but relative NMR shieldings do not improve much.
Whereas MPW1MPW91 seems better for inorganic bicycles than does B3LYP,
going from HF to DF sometimes makes the GIAO shielding differences worse.
For phosphorus (and selenium) I am using the Ahlrichs basis sets with a
single polarisation function, usually either MPW1MPW91/SVP or
RHF/TZV.  Adding more polarisation functions seems to make the shieldings
worse also.  

Optimising the geometries at a higher level seems to make more difference
than going to higher level on the GIAO calculations.

  Bruce Tattershall

Personal telephone no.: 00 44 191 222 6634
Personal Email: [email-masked]
Postal address:
    Dr. B.W. Tattershall    Department of Chemistry
    University of Newcastle    Newcastle upon Tyne    England

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From: Elie Giraud <[email-masked]>
Date: Mon, 05 Feb 2001 16:44:51 +0100

Dear CCLers,

I want to graph the De Jong GA test function called Schekel's Foxholes.
I'm looking for a freeware to do the job or a ready for use image
(preferably a colour picture).

Thanks in Advance

Best Regards,

E. 

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