From owner-chemistry@ccl.net Tue Jan 13 05:29:00 2009
From: "John M Simmie john.simmie- -nuigalway.ie" <owner-chemistry|-|server.ccl.net>
To: CCL
Subject: CCL:G: how to calc. BDE
Message-Id: <-38422-090113052443-25160-Q273KA54uBemTnHAVaNKSg|-|server.ccl.net>
X-Original-From: "John M Simmie" <john.simmie%x%nuigalway.ie>
Date: Tue, 13 Jan 2009 05:24:39 -0500


Sent to CCL by: "John M Simmie" [john.simmie*|*nuigalway.ie]
Sachin
A number of different methods & models possible; suppose you want to calculate the BDE of the CH bond in the side-chain methyl group of 2-methylfuran (2MF) then you need to compute the enthalpy of H-atom, 2-methylfuran and the radical as well to get 
BDE = H(H-atom)  H(radical)  H(2MF) 
converting atomic units into kJ/mol by multiplying by 2625.5

Use the best level of theory compatible with your computational resources and size of molecule  often this is the most difficult aspect of the whole problem.   For smallish molecules I tend to use CBS-QB3 multilevel theory which is built into Gaussian-03 and is easy to use & capable of good results, but, much depends upon your particular system.  Errol Lewar's book "Computational Chemistry" published by Kluwer is a very good guide

John Simmie::Combustion Chemistry Centre::National University of Ireland, Galway