Subject: Intramolecular Hydrogen Bond and AIM

From: Ari Lahti IFK <[email-masked]>
Date: Mon, 9 Dec 1996 16:30:38 +0200 (EET)

Dear CCLers,

I make calculations on a small molecule that has an imidazole ring and 
another ring formed by an intramolecular hydrogen bond. I would like to 
evaluate the strength of this intramolecular hydrogen bond, and I'm
wondering if the AIM theory might be useful in this respect. 

The charge density at the critical point of a bond is supposed to correlate
with the strength of the bond. Is this correlation linear in the sense that
it lets one compare the strengths of intramolecular hydrogen bonds between 
related molecules? Would this linearity make possible the evaluation of the
strength of an intramolecular hydrogen bond in absolute terms also,
through comparison of the charge density at the critical point of the
system under investigation to that of a known model system? 

I have made some preliminary calculations using the AIM card of
Gaussian94. My calculations always end up with 'Hopf-Poincare condition not 
satisfied', possibly because the program cannot handle the ring structures 
of my molecule. The ring points are thus not given. However, the critical
points of the covalent bonds and the intramolecular hydrogen bond are
indicated. Are these results useful, or does the Hopf-Poincare error
message mean that even data concerning these bond critical points are 
corrupted? 

	regards 
	--ari lahti

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* Ari Lahti, M.D., M.Sc.                          phone: +358 2 2654951     *
* Dept. of Phys. Chem.                            fax:   +358 2 2654706     *
* Abo Akademi University                          email: [email-masked]    *
* Porthansg. 3-5                                                            *
* FIN - 20500 Abo                                                           *
* Finland                                                                   *
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