Subject: THF values for COSMO calculations

From: [email-masked] (Douglas A. Smith Ph.D.)
Date: Thu, 31 Oct 1996 13:14:47 -0500

Another summary long overdue.

Doug

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My original message:

We are doing some MOPAC 93/COSMO calculations and need the following
information, if anyone has it.

(1) Dielectric constant for THF (tetrahydrofuran)
(2) Solvent radius for THF (the value used for RSOLV)

Thanks in advance.

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The dielectric constant for THF is reported to be 8.2 in a paper that I was
reviewing for the publication in JACS.

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11.6 (-70 C), 7.58 (25 C). Source: John A. Dean, "Handbook of Organic
Chemistry", 1987, McGraw-Hill, Inc.

Radius? I don't know.

Yong

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the dielectric constant for thf at 25c is 7.6

Louis Lalas
Regulatory Affairs Analyst, VWR Scientific Products  

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You asked about:

>(1) Dielectric constant for THF (tetrahydrofuran)
>(2) Solvent radius for THF (the value used for RSOLV)

for use with COSMO in MOPAC.  The dielectric constant for THF is 7.32
(according to my Chemist's Companion handbook), but the RSOLV value is not
so readily defined.  According to the article in J. Chem. Soc. Perkin Trans
2, 1993, p802 by A. Klamt and G. Schuurmann, R(solv) is an upperlimit for
the minum distance to a solute atom and:

"The most reliable value for each solvent has to be found empirically."

I have played with this some, and actually just using a value of 1 seems to
work as well as anything for the properties I was evaluating.  As I
understand it, R(solv) relates more to the radius of a local dipole (which
may interact with the solute) of the solvent molecule, rather than the
overall solvent molecule radius.  Also, conventional wisdom is that when
dealing with ions, a larger value for the radius is necessary, although I
haven't observed this myself.

I would be interested in a summary, if any of your replies outlines an
appropriate way to come up with R(solv) values.  Otherwise, I'd suggest you
just try using 1 as the value.

Ernest Chamot
Consultant in Computational Chemistry Applications
Chamot Laboratories, Inc.
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