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Dear CCLers,
Below is a summary of responses
to the "NICS(Negative nucleus-independent chemical shift)". In
the pursuit of the reliable definition of "aromaticity", Schleyer and
coworkers have proposed the NICS (JACS 1996, 118, 6317). Thanks to all who have
responded.
1) I am not 100% sure that I have
calculated NICS correctly, but I believe I
have. Using Gaussian, it is
trivial to include a ghost atom (symbol Bq)
at the geometric center of a
ring, or wherever one wishes to measure the
chemical shift. By default,
this atom will have no basis functions, but
will be used as a point at which
to calculate any desired property. Then,
by running a normal NMR
calculation, one obtains the chemical shifts for
all atoms, including the
ghost atom. Using this method, I have reproduced
results from the
recent Jial et al. paper in JACS 1997, 119, 5921 - 5929,
as well as the
original NICS paper (Schleyer et al. JACS 1996, 118, 6317 -
6318), so I
believe I am doing it
correctly.
Regards,
Eric
#########################################################################
>From
the desk of:
Dr. Eric V. Patterson
Postdoctoral Associate
Department of Chemistry voice: (612) 624-1535
University of Minnesota
FAX: (612) 626-7541
207 Pleasant St. SE email: patter.,at,.pollux.chem.umn.edu
Minneapolis,
MN 55455 WWW: http://pollux.chem.umn.edu/~patter
2) After reading your
NICS-question, I hope that I can give you a brief view
of calculating
NICS.
With Gaussian94 (also Gaussian92/DFT) it is very easy. A input for
benzene
is given below. It is like a normal Gaussian
job.
$RunGauss
# RHF/6-31+G* NMR Test Name=XXX
C6H6//RBECKE3LYP
6-31G(D)
0 1
C 0.00000 0.00000 0.00000
C 1.39659 0.00000
0.00000
C 2.09488 1.20948 0.00000
C 1.39659 2.41896 0.00000
C 0.00000
2.41896 0.00000
C -0.69829 1.20948 0.00000
H -0.54351 -0.94139
0.00000
H 1.94010 -0.94139 0.00000
H 3.18190 1.20948 0.00000
H 1.94010
3.36035 0.00000
H -0.54351 3.36035 0.00000
H -1.78532 1.20948
0.00000
Bq 0.69829 1.20948 0.00000 (in the center)
Bq 0.69829 1.20948
0.50000 (0.5A above the center)
Bq 0.69829 1.20948 1.00000 (0.5A above the
center)
Bq 0.69829 1.20948 1.50000 (1.0A above the center)
Bq 0.69829
1.20948 2.00000 (1.5A above the center)
Bq 0.69829 1.20948 2.50000 (2.0A
above the center)
You can calculat the NICS not only at the ring center,
but also above the
ring center (also every point you wish)
We
recommand the 6-31+G* basis set, but you can use another basis sets dependingon
the systems used and your CPU time.
In the keyword line, NMR means by
default NMR=GIAO.
In the output file, you will find the calculated
magnetic shielding constant at
the every point you have chosen. With sign
conversion, e.g., the negative of
the magnetic shielding is the NICS (in
agreement with 1H chemical shifts).
For the regular and plane molecules,
it is not difficult to find the geometricalpoint, but you will have trouble with
non-plane or 3D-molecules. For this purpose, I strongly recommand the molecule
program written by Dr. Hommes. This programhas many advantage over many other
softwares. You can contact him to get more
information (hommes.,at,.ccc.uni-erlangen.de). This
will help not only for NICS
calculations, but also for generating Gaussian
inputs, as well as for visualizing your optimized geometry and vibration model,
and drawing high quality plots for your publication.
If you have
another question, please let me know.
Sincerely yours
Dr. Haijun
Jiao
Computer Chemistry Center
Institut fuer Organische
Chemie
Universitaet Erlangen-Nuernberg
Henkestr.
42
91054-Erlangen
Germany
e-mail: haijun.,at,.ccc.uni-erlangen.de
Fax:
0049-9131-85-6533
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