WATOC Newsletter

February 1996

Edited by Paul G. Mezey

Vice-President of WATOC

Professor Leo Radom, Vice-President of WATOC, is the recipient of the 1994 Schrödinger Medal of WATOC

The 1994 Schrödinger Medal, a special award of WATOC for outstanding contributons to Theoretical Chemistry, has been given to Professor Leo Radom, Vice-President of WATOC. Professor Radom, of the Australian National University, has made ground-breaking research in the area of theoretical molecular structure determination.

Leo Radom was born on December 13, 1944 in Shanghai, China. At age two, he moved to Sydney where he spent most of his early years. He has obtained the Bachelor of Science degree with First Class Honours and the University Medal at the University of Sydney in 1965. Also at the University of Sydney, he completed a Ph.D. in 1969 in the general area of physical organic chemistry with the late R. J. W. Le Fèvre, making structural predictions on the basis of measurements of the electrical birefringency of molecules. During a 3 1/2 year postdoctoral period on a Fulbright Fellowship with Professor John Pople at Carnegie-Mellon University in Pittsburgh, Dr. Radom's principal interest has become theoretical chemistry. In 1972, Dr. Radom returned to Australia via a Queen Elizabeth II Fellowship at the Research School of Chemistry of the Australian National University where he currently holds the position of Professor. He has held numerous visiting professorships at many major universities, including the University of California, Irvine and Berkeley, the Ben Gurion University, Beer Sheva, the Institute of Molecular Science, Okazaki, The Hebrew University, Jerusalem, and the National University of Singapore. Professor Radom's achievements have been recognized through the award of the Rennie Medal, the H. G. Smith Medal and the Archibald Olle Prize of the Royal Australian Chemical Institute, the Mulliken Lecture Award of the University of Georgia, and through election to the Australian Academy of Science and the International Academy of Quantum Molecular Science.

Professor Leo Radom has made important advances in the study of the structures and stabilities of molecules and the mechanisms of reactions in which they are involved by use of ab initio molecular orbital theory. His innovative applications of quantum chemistry calculations both to rationalize existing chemistry and to predict new chemistry are building new bridges between theory and experiment. His early computations on substituent effects used an effective combination of quantitative ab initio molecular orbital theory and qualitative perturbation molecular orbital theory, and have served as templates for many subsequent works, including his advances that provided compelling evidence in favor of hyperconjugation.

Professor Radom's research has been a major factor in the assessment of theoretical procedures, i.e. determining what level of theory is required to obtain satisfactory results for the particular problem at hand. Dr. Radom has identified and rationalized circumstances in which the widely used Møller-Plesset perturbation expansion converges poorly, and suggested important safeguards.

Professor Leo Radom has carried out important research in the area of gas-phase ion chemistry, where one of his aims has been to demonstrate to the experimental gas-phase ion chemistry community the benefits of enhancing a synergistic relationship between theory and experiment. Dr. Radom's calculations have predicted the existence of many new ions, and in several cases these predictions have already been verified through experiments, such as mass spectrometry. Dr. Radom's discovery that radical cations in which the radical and charge sites are located on different centers (he calls these "distonic radical cations") often display a surprising stability with respect to unimolecular decomposition which contrasts with the instability of the neutral parent molecules from which they are formally derived. His calculations on gas-phase ions also contributed to the discovery in interstellar space of the isoformyl cation HOC+. Dr. Radom's calculations predicted that the tetraheliomethane tetracation (CHe44+) is a stable species which is potentially observable in a mass spectrometer, and that the methane dication is planar but not square.

Our understanding of reaction processes in the research laboratory, in industry, and in the atmosphere is greatly enhanced if reliable thermochemical information is available. Professor Radom has carried out a wide variety of theoretical thermochemical studies, some of which have led to the recent resolution of a major conflict in the experimental literature regarding gas-phase proton affinity scales, and to a subsequent reassignment of the experimental heat of formation for the tert-butyl cation, an important prototype species.

In one of his more recent studies, Professor Radom has developed a new strategy for designing neutral saturated hydrocarbons that may contain a planar, tetracoordinate carbon atom, leading to the alkaplane family of molecules. This research has revealed remarkable properties for such molecules including ionization energies comparable to those of the alkali metals lithium and sodium, and proton affinities greater than that of 'proton sponge", with important implications for synthetic chemistry.

The work of Professor Leo Radom, the winner of the 1994 Schrödinger Medal of WATOC, serves as an inspiration to all theoretical chemists.

Paul G. Mezey

Vice-President, WATOC

Theoretical Breakthrough in Azulene Photochemistry

The research team of Bernardi and Robb has reported a computational chemistry breakthrough (J. Amer. Chem. Soc., 118, 169, 1996) that provides an explanation of a question that has puzzled experimental photochemists for many decades. The new results give convincing evidence that some of the unusual photochemical properties of azulene are caused by an exceptionally fast decay of the S1 state via a conical intersection, as predicted by Longuet-Higgins. The calculations indicate that the decay takes place on the femtosecond scale, apparently before a single "semi-classical" S1 oscillation can be completed! Theoretical chemistry is on the fast track!

C-H Rupture Leads to Hot Ground State

Dunn and Morokuma have reported ground-breaking theoretical results on the detailed mechanisms of N-H, C-N, and C-H bond ruptures of an important prototype molecule, methylamine (J. Phys. Chem., 100, 123, 1996). The detailed theoretical mechanisms of photochemical processes leading to these bond ruptures explain the relevant experimental findings. The C-H rupture in methylamine leads to a hot ground state, with implications for subsequent processes. The study fully validates the theoretical-computational approach to complex photochemical reactivity problems.

Ab initio Quality Electron Densities Beyond the 1500 Atom Limit

As reported in C&EN News, Aug. 14, 1995, and in the original publication (J. Math. Chem., 17, 203, 1995), the MEDLA Computational Microscope method, based on a Hartree-Fock 6-31G** basis implementation of the Additive Fuzzy Density Fragmentation principle, has been applied to calculate the first ab initio quality, high resolution electron densities for a molecule beyond the 1500 atom limit, surpassing the earlier size record obtained for a smaller protein by the same group (J. Amer. Chem. Soc., 116, 12022, 1994). The resolution of the Computational Microscope image of the largest molecule studied to date, the protein HIV-1 protease monomer of 1564 atoms, exceeds current X-ray resolution by about two orders of magnitude.



July 7 - 12, 1996


Prof. Amiram Goldblum, Dept. Pharmaceutical Chemistry, School of CHAIRMAN - WATOC '96 Pharmacy, Hebrew Univ. Jerusalem, Jerusalem, Israel 91120

Fax: 972-2-410 740 (also 972-2-784-010)

E-mail: amiram@vms.huji.ac.il

Prof. Yitzhak Apeloig, Dept. Chemistry, Technion - Israel Institute of PROGRAM CHAIRMAN Technology, Haifa, Israel 32000

Fax: 972-4-237 599 (also 972-4-233 735)

E-mail: chdean@techunix.technion.ac.il