Subject: Summary: heats of fusion

From: "Dr. D.Eric Walters" <[email-masked]>
Date: Thu, 15 Dec 1994 13:30:47 -0600 (CST)

Here is a summary of replies to my question about calculating heats of 
fusion.  Thanks to those who replied!

Message 1/3  From Lawrence R. Dodd                   Dec 7, 94 01:32:59 
pm -0500

Date: Wed, 7 Dec 94 13:32:59 -0500
To: [email-masked]
Subject: Re: CCL:calculating heat of fusion?
X-Attribution: lrd
Reply-To: [email-masked]

::: "DEW" == D Eric Walters <[email-masked]> writes:

  DEW> Are there methods for calculating heat of fusion (crystal
  DEW> melting) for different crystal forms of small organic
  DEW> compounds?

Perhaps you meant `melting' and you probably already know this, but
the heat of fusion (aka heat of melting) and heat of crystallization
differ by the heat of solution.  Often one is approximated by the
other but they are different thermodynamically.

-----------------------------
Eric-The heat of fusion would be a difficult problem because you would
have to have a good model of the liquid state structure.  The heat of
sublimation(crystal to vapor transformation) is easier to compute. We've
discussed this in JACS 1994,116,455-470(see p. 458 in particular). Basically
what you do is to compute the interaction energy between an aribitrary
molecule in the packed crystal structure and all the other molecules using
an appropriate atom-atom potential forcefield.  We have code written for
this using the MM2 forcefield or the CFF91 forcefield. The code requires
packing the structure using CHEMX/CHEMLIB modeling package.  If you have
these, I can send you the rest.
 ***************
 Jerry Perlstein
 Center for Photoinduced Charge Transfer
 Department of Chemistry
 University of Rochester
 Rochester,NY 14627-0216
--------------------------
A method for the calculation of entropies and enthalpies of fusion is
described in J. S. Chickos, et.al., J. Org. Chem. 1991, 56, 927-938.

Peter W. Rose,
Computational Chemistry
Agouron Pharmaceuticals, Inc.
email: [email-masked]

-------------------------

* D. Eric Walters, Ph.D., Associate Professor, Biological Chemistry
* Finch University of Health Sciences/The Chicago Medical School
* 3333 Green Bay Road, North Chicago, IL  60064
* ph 708-578-3000, x-498;fax 708-578-3240; email: [email-masked]
* "A man would do nothing if he waited until he could do it so well that
*  no one would find fault with what he had done." --Cardinal Newman