CCL:G: Natural Resonance Theory Calculations

From: Italo Anjos <italocurvelo=-=gmail.com>
Subject: CCL:G: Natural Resonance Theory Calculations
Date: Thu, 5 Jan 2012 20:13:55 -0300

Hello,

I' ve been running some NRT (Natural Resonance Theory) calculations using NBO 5.9/ Gaussian g09. For most compounds, analysis seem to be successful as they find many canonical structures and display their respective weightings. But for a few molecules, NBO seems unable to determine the resonance structures and output displays the following message:

No covalent reference structures found; abandon NRT analysis

All calculations were made for a set of sulphur-containing heterocyclic compounds. It seems odd that for some of them, NBO found dozens of canonical structures and it found none for the others.

Could anyone help me with this problem?

I appreciate any help.

Regards,

Italo