Computational Quantum Chemistry

                   

Principal Investigator

Leo Radom

Research School of Chemistry

Chemistry is traditionally an experimental science. However, recent advances in computational
techniques and the development of highly efficient computer algorithms allows the computer to provide a powerful complement to experiment in the study of the chemistry of small molecules. Theory may particularly be used to advantage for reactive or unstable species for which appropriate laboratory experiments are difficult to perform, and these are therefore the systems on which we focus attention. The principal properties of molecules which we examine are their structures, i.e. their shape in terms of bond lengths and bond angles, and their stabilities, i.e. an assessment of whether the molecules are likely to be long-lived or whether they are likely to decompose easily. We also calculate spectroscopic properties. These are particularly useful as fingerprints for eventual experimental identification (e.g. in the laboratory or in interstellar space) of molecules which have hitherto not been observed.
 

Co-Investigators

       

Andrew Chalk

James Gauld

Paul Mayer

Mark McDonald

Christopher Parkinson

Danne Rasmussen

Anthony Scott

David Smith

Research School of Chemistry

Michelle Coote

Hans Heuts

University of New South Wales

Athanassios Nicolaides

Mie University, Japan

Brian Smith

Biomolecular Research Institute,

Melbourne

Richard Wong

National University of Singapore

       
               

   
               

What are the results to date and the future of the work?

During 1997, our computational research focussed on the following principal themes: gas-phase ion chemistry, organic reactive intermediates, radical cation chemistry, theoretical thermochemistry, planar tetracoordinate carbon, nucleophilic substitution reactions, enzyme-mediated reactions, free radical chemistry, phosphorus exchange reactions and polymerization.

We will continue to use theory to examine the properties of reactive species for which appropriate experimental measurements are difficult. We hope that our predictions will continue to stimulate relevant experiments. In the longer term, the computer calculations may prove useful in the design of new materials and pharmaceuticals.

Projects

k29, p03, q07, q08, r54, s08, v01, v55, v56 ­ VPP, PC

   
               
                   
Appendix A -

                   
     

What computational techniques are used?

The ab initio molecular orbital calculations required to provide reliable information on molecular structures and reaction mechanisms are extremely computationally intensive. The program packages that we use include Gaussian 94, ACES II and MOLPRO.

Publications

C. Aubry, M. J. Polce, J. L. Holmes, P. M. Mayer, L. Radom, Dimethylcarbene: Its Radical Cation and Dication, Journal of the American Chemical Society, 119, 1997, 9039­9041.

 

J. P. Blaudeau, M. P. McGrath, L. A. Curtiss, L. Radom, Extension of Gaussian-2 (G2) Theory to Molecules Containing Third-Row Atoms K and Ca, Journal of Chemical Physics, 107, 1997, 5016­5021.

A. J. Chalk, L. Radom, Proton-Transport Catalysis: A Systematic Study of the Rearrangement of the Isoformyl Cation to the Formyl Cation, Journal of the American Chemical Society, 119, 1997, 7573­7578.

J. Cioslowski, A. P. Scott, L. Radom, Catastrophes, Bifurcations and Hysteretic Loops in Torsional Potentials of Internal Rotations in Molecules, Molecular Physics, 91, 1997, 413­420.

A. L. L. East, L. Radom, Ab Initio Statistical Thermodynamical Models for the Computation of Third-Law Entropies, Journal of Chemical Physics, 106, 1997, 6655­6674.

A. L. L. East, B. J. Smith, L. Radom, Entropies and Free Energies of Protonation and Proton-Transfer Reactions, Journal of the American Chemical Society, 119, 1997, 9014-9020.

J. W. Gauld, L. A. Eriksson, L. Radom, An Assessment of Procedures for Calculating Radical Hyperfine Structures, Journal of Physical Chemistry A, 101, 1997, 1352­1359.

J. W. Gauld, J. L. Holmes, L. Radom, An Evaluation of Additivity Schemes for the Estimation of Heats of Formation of Distonic Radical Cations, Acta Chemica Scandinavica, 51, 1997, 641­645.

J. W. Gauld, L. Radom, Accurate Theoretical Structures of Radical Cations Containing Unusually Long Bonds: The Structures of CH3CH2OH·+, CH3HH2 and H2CH2H2, Chemical Physics Letters, 275, 1997, 28­34.

J. W. Gauld, L . Radom, Effects of Neutral Bases on the Isomerization of Conventional Radical Cations CH3X·+ to Their Distonic Isomers H2H (X = F, OH, NH2): Proton-Transport Catalysis and Other Mechanisms, Journal of the American Chemical Society, 119, 1997, 9831-9839.

P. M. Mayer, J. F. Gal, L. Radom, The Heats of Formation, Gas-Phase Acidities, and Related Thermochemical Properties of the Third-Row Hydrides GeH4, AsH3, SeH2 and HBr from G2 Ab Initio Calculations, International Journal of Mass Spectrometry and Ion Processes, 167/168, 1997, 689­696.

     
- Appendix A

 
     
       

P. M. Mayer, M. N. Glukhovtsev, J. W. Gauld, L. Radom, The Effects of Protonation on the Structure, Stability and Thermochemistry of Carbon-Centered Organic Radicals, Journal of the American Chemical Society, 119, 1997, 12889­12895.

P. M. Mayer, C. J. Parkinson, D. M. Smith, L. Radom, An Assessment of Theoretical Procedures for the Calculation of Reliable Free Radical Thermochemistry. A Recommended New Procedure, Journal of Chemical Physics, in press.

P. M. Mayer and L. Radom, An Ab Initio Study Concerning the Experimental Observability of C3H62+ Isomers, Chemical Physics Letters., 280, 1997, 244­250.

A. Nicolaides, L. Radom, Classical and Non-Classical Isomers of Tropylium, Silatropylium and Germatropylium Cations. Descending the Periodic Table Increases the Preference for Non-Classical Structures, Journal of the American Chemical Society, 119, 1997, 11933­11937.

A. Nicolaides, D. M. Smith, F. Jensen, L. Radom, Phenyl Radical, Cation and Anion. The Triplet-Singlet Gap and Higher Excited States of the Phenyl Cation, Journal of the American Chemical Society, 119, 1997, 8083­8088.

L. Radom, M.W. Wong, A. Pross, Radical Additions to Alkenes: A Theoretical Perspective, In Advances in Free Radical Polymerization, ACS Symposium Series, (Ed. K. Matyjaszewski), American Chemical Society, Washington, DC, in press.

A. P. Scott, I. Agranat, P.U. Biedermann, N.V. Riggs, L. Radom, Fulvalenes, Fulvenes and Related Molecules: An Ab Initio Study, Journal of Organic Chemistry, 62, 1997, 2026­2038.

A. P. Scott L. Radom, Ketene and Ketene Radical Cation: The Unusual Effect of Methyl and Dimethyl Substitution, International Journal of Mass Spectrometry and Ion Processes, 160, 1997, 73­81.

       
Appendix A -