Subject: correction: HOMO/LUMO & entropy energy

From: Ning Xie <[email-masked]>
Date: Sat, 10 Jan 1998 01:39:58 -0600 (CST)

Hi, there, thank you all for your attention, especially thank Alan and 
Karl for their replies.
Maybe I did not make myself clear. I am studying the oxidation reaction
of para-substituted phenyl methyl sulfides and the corresponding
sulfoxides by permanganate-zinc chloride complex (MnO4- ZnCl2). I am using
ab initio method (gaussian 94) to calculate the HOMO of surfur compounds
and the LUMO energy of the oxidant. The energy gap between the LUMO of the
oxidant and the HOMO of the reductant (sulfur compound) correlate well
with the free energy of activation obtained experimentally, i.e. as the
substituents change from methoxy to methyl, to hydrogen, to fluoro, to
chloro, to nitro the HOMO gets lower and the energy gap gets larger and
free energy of activation becomes higher. This obervation agrees with the
Frontier Molecular Orbital Theory. However, somebody argues that the
calculation does not take entropy effect into consideration so the energy
gap should correlate well with the enthalpy of activation rather than with
the free energy of activation. This is why I need to know if the
calculated HOMO or LUMO energy has anything to do with entropy. All
compounds are in ground states and LAN2DZ basis set is used for the
oxidant complex and the 6-31G(d) is used for sulfur compounds.
Any comment is greatly appreciated. Thank you for your help.

=========================================================================
|  NING  XIE                         Tel: (306)585-5262 (O)             | 
|  Chemistry Department                   (306)585-2184 (H)             |
|  University of Regina              Fax: (306)585-4894                 |
|  Regina, SK                     E-Mail: [email-masked]   |
|  Canada   S4S 0A2                                                     |
=========================================================================