Dear Sutar,

You can run ab initio, DFT (with a variety of bases sets) or semi-empirical such as AM1 or PM3 calculations (all these programs are installed in Gaussian 09) in which you conduct a reaction coordinate method on the bond N-H or O-H (you should increase the bond by 0.1 A until reaching the product; about 20 cycles each of 0.1 A). The reaction coordinate method should give you an energy profile which starts from the original bond distance, N-H or O-H until complete dissociation. Along the energy profile you should locate a transition state (TS) which can be confirmed by a frequency calculation to the geometry at the maximum of the energy profile.

Please note that all frequencies for the reactants, products and intermediates are positive and the frequencies for TS all are positive except for one frequency which should be negative.

The difference between the energies (enthalpy and entropy= free) of TS and GM (global minimum structure of the reactant) should give you the dissociation energy.

For papers reported on such calculations, please see the following links:

http://onlinelibrary.wiley.com/doi/10.1002/cjoc.200590194/abstract

Hoping this will be helpful,

Rafik

Dear Sutar

A paper on: Assessment of Performance of G3B3 and CBS-QB3 Methods in

Calculation of Bond Dissociation Energies.By: QI, Xiu-Juan(亓秀娟) FENG, Yong(封勇) LIU, Lei(刘磊) GUO, Qing-Xiang*(郭庆祥). Assessment of Performance of G3B3 and CBS-QB3 Methods in Calculation of Bond Dissociation Energies, is in attach.

Best regards

Dear Talaat,

The paper you indicated is the same paper I attached to my first answer.

Rafik

Dear Rafik,After revision of the paper that i've sent and the cite you've puted, i found that they are the same. Thank u for ur remark.

Dear, Kashinath Sutar , Please, find in attach, a paper on: Dissociation Energies of O−H Bonds of Phenols and Hydroperoxides by: Denisov Evgeny and Denisova Taisa

Institute of Problems of Chemical Physics RAS.Russia. Application of Thermodynamics to Biological and Materials Science.

Best wishes

Mr. Sutar,

You could pay attention to this paper:

1. Theoretical Chemistry Accounts, 1998, 99, 171-174

Computational studies of bond dissociation energies, ionization potentials, and heat of formation for NH and NH+. Are hybrid density functional theory methods as accurate as quadratic complete basis set and Gaussian-2 ab initio methods?, B. Jursic,

Everything is writen there.