Computational Quantum Chemistry

 

 

Principal Investigator

Leo Radom

Research School of Chemistry

Co-Investigators

Andrew Chalk

Michael Hartmann

Christopher Parkinson

Danne Rasmussen

Axel Schulz

Anthony Scott

Stefan Senger

David Smith

Research School of Chemistry

Michelle Coote

Hans Heuts

University of New South Wales

Brian Smith

Biomolecular Research Institute, Melbourne

Projects

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

             
 

 

Chemistry is traditionally an experimental science. However, recent advances in computational techniques and the development of highly efficient computer algorithms allows the computer, through quantum mechanical calculations, to provide a powerful complement to experiment in the study of the chemistry of small to medium-sized 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 examine the mechanisms of chemical reactions, i.e. determine the preferred pathways along which reactions proceed.

 
                 

   
                 
                     

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

During 1998, our computational research focussed on the following principal themes: gas-phase ion chemistry, organic reactive intermediates, theoretical thermochemistry, planar tetracoordinate carbon, nucleophilic substitution reactions, enzyme-mediated reactions,

 
                     
Appendix A -

                     

       

free radical chemistry, phosphorus exchange reactions and polymerization. Details may be found in the publications listed below. The field of computational quantum chemistry received special recognition during the year with the award of the 1998 Nobel Prize in Chemistry to Professor John Pople, a frequent visitor to the group from Northwestern University, for his pioneering research in the area.

We will continue to use theory to examine the properties of reactive species for which appropriate experimental measurements are difficult, and to study the mechanisms of chemical reactions. 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.

What computational techniques are used?

The ab initio molecular orbital calculations required to provide reliable information on molecular sctructures and reaction mechanisms are extremely computationally intensive. The program packages that we use include GAUSSIAN 98, ACES II and MOLPRO.

Publications

A. J. Chalk, L. Radom, The Importance of Ion-Neutral Complexes in Gas-Phase Ionic Reactions: Fragmentation of [CH3CH2OCH2]+ as a Prototypical Case, Journal of the American Chemical Society, 120, 1998, 8430-8437.

A. J. Chalk, L. Radom, Ion-Transport Catalysis: Catalyzed Isomerizations of NNH+ and NNCH3+, Journal of the American Chemical Society, in press.

M. L. Coote, T. P. Davis, L. Radom, The Effect of Remote Substituents in Free Radical Addition Reactions: New Evidence for the Penultimate Unit Effect, Journal of Molecular Structure, Theochem, in press.

M. L. Coote, T. P. Davis, L. Radom, Effect of the Penultimate Unit on Radical Stability and Reactivity in Free-Radical Polymerization, Macromolecules, in press.

       

B. J. Duke, L. Radom, Gaussian-2 (G2) Theory for Third-Row Elements: A Systematic Study of the Effect of the 3d Orbitals, Journal of Chemical Physics, 109, 1998, 3352­3359.

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, 108, 1998, 604­615.

P. M. Mayer, L. Radom, Deprotonating Molecules and Free Radicals to Form Carbon-Centered Anions: A G2 Ab Initio Study of Molecular and Free Radical Acidity, Journal of Physical Chemistry, 102, 1998, 4918­4924.

P. M. Mayer, M. S. Taylor, M. W. Wong, L. Radom, Thermochemistry of CH3CN, CH3NC and Their Cyclic Isomers, and Related Radicals, Cations and Anions: Some Curious Discrepancies Between Theory and Experiment, Journal of Physical Chemistry, 102, 1998, 7074­7080.

       
- Appendix A

 
       

       

M. L. McKee, P. M. Mayer, L Radom, An Ab Initio Study of Ionised Cyclobutanone and Cyclopentanone. Comparison of the Thermodynamic and Kinetic Stabilities of the Distonic Isomers H2(CH2)n=O, European Mass Spectrometry, 4, 1998, 23­30.

C. J. Parkinson, P. M. Mayer and L. Radom, Cyanovinyl Radical: An Illustration of Poor Performance of Unrestricted Perturbation Theory and Density Functional Theory Procedures in Calculating Radical Stabilization Energies, Theoretical Chemistry Accounts, in press.

L. Radom, M. W. Wong, A. Pross, Radical Additions to Alkenes: A Theoretical Perspective, In Controlled Radical Polymerization, ACS Symposium Series 685, K. Matyjaszewski, Editor, pp 31­49, American Chemical Society, Washington, DC, 1998.

D. R. Rasmussen, L. Radom, The Planar Carbon Story, Pure and Applied Chemistry, 70, 1998, 1977­1984.

A. P. Scott, B. T. Golding, L. Radom, Remarkable Cleavage of Molecular Hydrogen Without the Use of Metallic Catalysts, New Journal of Chemistry, 1998, 22, 1171­1173.

B. J. Smith, L. Radom, The Heat of Formation of t-Butyl Radical, Journal of Physical Chemistry, 102, 1998, 10787-10790.

D. M. Smith, A. Nicolaides, B. T. Golding, L. Radom, Ring Opening of the Cyclopropylcarbinyl Radical and its N- and O-Substituted Analogues: A Theoretical Examination of Very Fast Unimolecular Reactions, Journal of the American Chemical Society, 120, 1998, 10223­10233.

D. M. Smith, B. T. Golding, L. Radom, On the Mechanism of Action of Vitamin B12: Theoretical Studies of the 2-Methyleneglutarate-Mutase-Catalyzed Rearrangement, Journal of the American Chemical Society, in press.

D. M. Smith, B. T. Golding, L. Radom, The Facilitation of Enzyme-Catalyzed Reactions by Partial Proton Transfer: Application to Coenzyme B12-Dependent Methylmalonyl-CoA Mutase, Journal of the American Chemical Society, in press.

T. I. Solling, M. A. McDonald, S. B. Wild. L. Radom, Novel Pi-Ligand Exchange and Insertion Reactions Involving Three-Membered Phosphorus Heterocycles: An Ab Initio Investigation, Journal of the American Chemical Society, 120, 1998, 7063­7068.

T. I Sølling, L. Radom, Exchange Reactions of Chloriranium Ions and Chlorirenium Ions: A G2 Investigation, International Journal of Mass Spectrometry, in press.

T. I. Solling, S. B. Wild, L. Radom, Exchange and Insertion Reactions Involving Borane Adducts of Phosphirane and Phosphirene: A G2(MP2) Ab Initio Investigation, Journal of Organometallic Chemistry, in press.

T. I Sølling, S. B. Wild, L. Radom, Are Pi-Ligand Exchange Reactions of Thiirenium and Thiiranium Ions Feasible? An Ab Initio Investigation, Chemistry ­ A European Journal, in press.

M. W. Wong and L. Radom, Radical Addition to Alkenes: Further Assessment of Theoretical Procedures, Journal of Physical Chemistry, 102, 1998, 2237­2245.

       
Appendix A -