Principal Investigator Leo Radom Projects k29, p02,p03, q07, q08, r54, r55, r56, s07, s08

Research School of Chemistry Machine VP

Co-Investigators A L L East, J W Gauld, H Heuts, D C Marsden, A Nicolaides, D R Rasmussen, A P Scott, D M Smith, Research School of Chemistry, M N Glukhovtsev, University of Sydney; B J Smith, Biomolecular Research Institute, Melbourne; J B Westmore, University of Manitoba and M W Wong, University of Queensland


Computational Quantum 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.


What are the basic questions addressed?

What are the structures of a variety of molecules of current interest and what are the mechanisms of reactions which they undergo? We use ab initio molecular orbital theory to study such problems.

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

During 1995, 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, isotope effects, free radical chemistry 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.

What computational techniques are used and why is a supercomputer required?

The ab initio molecular orbital calculations required to provide reliable information on molecular structures and reaction mechanisms are extremely computationally intensive.

Publications

Chemistry by computer: a theoretical approach to structure and mechanism, L. Radom, in "Organic Reactivity: Physical and Biological Aspects", B T Golding, R J Griffin, and H Maskill, Eds., pp 278-300, Royal Society of Chemistry, Cambridge (1995).

Ab initio calculations of the gas-phase acidities of diazirine and diazomethane, A.J. Russell, A.P. Scott and L. Radom, Australian Journal of Chemistry, 48, 401-405 (1995).

Gas-phase identity SN2 reactions of halide anions with methyl halides: A high level computational study, M.N. Glukhovtsev, A. Pross and L. Radom, Journal of the American Chemical Society, 117, 2024-2032 (1995).

Calculation of proton affinities using the G2(MP2,SVP) procedure, B.J. Smith and L. Radom, Journal of Physical Chemistry, 99, 6468-6471 (1995).

Extension of Gaussian-2 (G2) theory to bromine- and iodine-containing molecules: Use of effective core potentials, M.N. Glukhovtsev, A. Pross, M.P. McGrath and L. Radom, Journal of Chemical Physics, 103, 1878 (1995).

Radical addition to alkenes: An assessment of theoretical procedures, M.W. Wong and L. Radom, Journal of Physical Chemistry, 99, 8582-8588 (1995).

Determination of the chirality of enantiomeric [16O, 17O, 18O] sulfate esters by infrared spectroscopy: An ab initio evaluation, A. Nicolaides and L. Radom, Journal of the Chemical Society, Chemical Communications, 701-702 (1995).

Gas-phase SN2 reactions of halide anions at neutral nitrogen: A high level computational study, M.N. Glukhovtsev, A. Pross and L. Radom, Journal of the American Chemical Society, 117, 9012-9018 (1995).

Extension of Gaussian-2 theory to molecules containing third-row atoms Ga-Kr, L.A. Curtiss, M.P. McGrath, J.P. Blaudeau, N.E. Davis, R.C. Binning and L. Radom, Journal of Chemical Physics, 103, 6104-6113 (1995).

A priori prediction of propagation rate coefficients in free radical polymerizations: Propagation of ethylene, J.P.A. Heuts, R.G. Gilbert and L. Radom, Macromolecules, 28, 8771-8781 (1995).

Gas-phase acidities: A comparison of density functional, MP2, MP4, F4, G2(MP2,SVP), G2(MP2) and G2 procedures, B.J. Smith and L. Radom, Chemical Physics Letters, 245, 123-128 (1995).

Is the most stable gas-phase isomer of the benzenium cation a face-protonated p-complex? M.N. Glukhovtsev, A. Pross, A. Nicolaides and L. Radom, Journal of the Chemical Society, Chemical Communications, 2347-2348 (1995).

A comparison of high-quality ab initio basis sets: The inversion barrier in ammonia, A.L.L. East and L. Radom, Journal of Molecular Structure, in press.

Acidities, proton affinities and other thermochemical properties of hypohalous acids, HOX (X = F - I): A high level computational study, M.N. Glukhovtsev, A. Pross and L. Radom, Journal of Physical Chemistry, in press.

Fulvalenes, fulvenes and related molecules: An ab initio study, A.P. Scott, I. Agranat, P.U. Biedermann, N.V. Riggs and L. Radom, Journal of the American Chemical Society, submitted.

Gas-phase non-identity SN2 reactions of halide anions with methyl halides: A high level computational study, M.N. Glukhovtsev, A. Pross and L. Radom, Journal of the American Chemical Society, in press.

Gaussian-2 theory: Reduced basis set requirements, L.A. Curtiss, P.C. Redfern, B.J. Smith and L. Radom, Journal of Chemical Physics, in press.

An evaluation of the performance of G2, G2(MP2) and G2(MP2,SVP) theories for heats of formation and heats of reaction in the case of "large" hydrocarbons, A. Nicolaides and L. Radom, Molecular Physics, in press.