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HISTORICAL OVERVIEW John Anthony Pople: Cambridge Days A.
D.Buckingham
University Chemical Laboratory, Cambridge. CB2 1 E W,United Kingdom
This historical note surveys in words and pictures the scene in the Department of Theoretical Chemistry in Cambridge in the 1950s. with emphasis on the work of J. A. Pople. John Anthony Pople was born in Burnham on Sea in Somerset in The West of England on 31 October 1925. He was the elder son of Herbert Keith Pople and Mary Frances Pople (nee Jones). He was educated at Rristol Grammar School and at Trinity College Cambridge. He was a Research Student in Cambridge from 1948 to 1951 and his supervisor was Professor Sir John Lennard-Jones, F.R.S. He was awarded his Ph.D. in 1951 for a thesis entitled "Lone Pair Electrons". Figure I shows the building that housed the Department of Theoretical Chemistry until the move to Lensfield Road in 1958. The ground floor and the first floor were occupied by the Department of Physical Chemistry, whose Head was Professor R. G. W. Norrish, F.R.S.; the top floor, with attic type rooms, was home to the Theoretical Chemists. Lennard-Jones' office was at the southern end at the top of the stairs, S. F. Boys' room was nearby, and then came the large Seminar Room containing about IO desks where the research students and others worked. At the northern end of this room there was a door into a room that was occupied by G. G. Hall and J. A. Pople. Distinguished visitors would sometimes occupy one of the desks in the Seminar Room for up to a year. Professor J. G. Kirkwood was there for a while in 1955. The atmosphere was intellectual and serious, but friendly. It was taken for granted that the research had to be of high quality. Figure 2 is the first of the annual photographs showing John Poplc. The photograph was a serious matter for Lennard-Jones, and he was probably not pleased that his bright young research student was abent! Perhaps John Pople was having a piano lesson at the time-his piano teacher was Joy Bowers, and she and John were married in 1952. They lived in Thriplow, a beautiful village about seven miles south of Cambridge, and John would drive into town in his smart MG sports car. Figure 3 shows the Department in 1953/54. Frank Boys was in charge, and John Pople was a Fellow of Trinity College (he was elected in 1951). Among the visitors that year was Professor Robert G.Parr, and R. K. Nesbet was a research student of Frank Boys. In 1954 John Pople was appointed to a University Lectureship in Mathematics, and Christopher Longuet-Higgins came as Professor of Theoretical Chemistry in succession to LennardJones (Figure 4). Andrew Hurley returned to Cambridge from Australia as a Research Fellow of Trinity College, and among the visitors that year were B. J. Alder, A. G. McLellan, and R. L. Scott. In 1957-1958 John Pople was among those seated for the photograph (Figure 5 ) . as was Leslie Orgel, a new member of staff, and John Murrell (a Research Fellow of Corpus Christi College). The membership of the Department included J. S. Griffith, A. D. McLachlan, R. A. Sack, L. Salem, M. J. Stephen, and J. P. Valleau. Pople's first paper, "The molecular orbital theory of chemical valency. 1V. The significance of equivalent orbitals", by Sir John Lennard-Jones and J. A. Pople, was submitted on I6 December 1949,and published in the Proceedings of the Royal Society in 1950.' In Part I I of this series,2Lennard-Jones had shown how, in molecules with symmetry, the molecular orbitals could be transformed into equivalent orbitals which differ only in their
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Figure 1. The Department of Theoretical Chemistry occupied the top floor of this building at the south east end of Free School Lane in Cambridge in the 1950s. The Department moved to Lensfield Road in 1958.
orientation in the molecule. Lennard-Jones and Pople' showed how equivalent orbitals could be used to describe molecules whose atoms p s e s s inner shells and lone pairs and they illustrated the thcory by reference to H 2 0 and NH,; they pointed out the significance of lone pairs of electrons in determining the shapes of molecules. A second paper, "The molecular orbital theory of chemical valency. V. The structure of water and similar molecule^",^ was submitted on the same date as Part IV and is under Pople's sole authorship. It showed that the electronic structure of H 2 0 can be approximately described by two sets of two equivalent orbitals pointing in nearly tetrahedral directions (the OH bonds and the lone pairs); the lone pairs contribute substantiallyto the molecular dipole moment. In Part IX." Lennard-Jones and Pople considered the interaction of electrons in the same orbital. Their exact equations, based on ( I ) Lennard-Jones. Sir John; Pople, J. A. Proc. R. Soc. A 1950, 202, 166-1 80.
(2) Lennard-Jones, Sir John. Proc. R. Soc. A 1949, 198. 14-26. (3) Pople. J. A. Proc. R. Soc. A 1950,202.323-336. (4) Lennard-Jones, Sir John; Pople. J. A. Proc. R. Soc. A 1951. 210. 190-206.
0022-3654/90/2094-543 1 S02.50/0 0 I990 American Chemical Society
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The Journal of Physical Chemistry, Vol. 94. No. 14. 1990
Buckingham
Figure 2. The Department of Theoretical Chemistry in 1950. J. A. Pople (inset). (Standing) €3. Bhattacharya, J. L. Turner, V. E. Price, J. P. Teegan. L. A. G. Dresel. (Sitting) Mrs. K. Lenney. D. P. .lenkins, Dr. S. F. Boys. Prof. Sir John Lennard-Jones. G. G. Hall, J. K. Perring, Miss H. Pye.
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Figure 3. The Department of Theoretical Chemistry in 1954. (Backrow) C. M. Reeves. R. K. Nesbet, A. D. Buckingham, M. P.Schofield. (Front row) Mrs. B. M. Scott, Dr. J. A. Pople, Prof. R. G. Parr. Dr. S. F. Boys, Dr. G. G. Hall. Dr. V. E. Price. A. Brickstock.
J o h n Anthony Pople: Cambridge Days
The Journal of Phvsical Chemistry, Vol. 94,No. 14, 1990 5433
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Figure 4. The Department of Theoretical Chemistry in 1955. (Standing) M. P. Schofield, Dr. A. C. Hurley, Dr. R. L. Scott, A. D. Buckingham, J. N. Vurrell, M.de V. Roberts, 1. Shavitt, Dr. A. G. McLellan, Miss K. L. McEwen, Dr. J. A. Pople. Mrs. R. M.Scott, C. M. Reeves. (Sitting) Dr. S. F. Boys, Prof. H. C . Longuet-Higgins, Dr. G. G. Hall.
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Figure 5. The Department of Theoretical Chemistry in 1958. (Rack row) C. K. Jorgensen, M. J. Stephen, J. P. Valleau. L. Salem, R. A. Sack. (Middle row) D. A. Levy. J. S. Griffith. F. Halverson, A. D. McLachlan, C. Reid, P. M a n r . J. M. Foster, I. Jones. (Front row) Miss M. G. Cannon, Dr. L. E. Orgel, Dr. S. F. Boys, Prof. H. C. Longuet-Higgins. Dr. J. A. Poplc, Dr. J. N. Vurrell. Mrs. Y. V. Targonski. Absent: T. W. Marshall.
5434 The Journal of Physical Chemistry, Vol. 94, No. 14, 1990 expansions of the wave function and interelectronic repulsion term in the Hamiltonian over the irreducible representations of the symmetry group, provided a means of comparing approximate wave functions and in particular the molecular orbitals and the “electron-pair function” based on the HeitlerLondon description of the hydrogen molecule. A further important step in this direction was taken in Part XVI by Hurley, Lennard-Jones, and Pople’ whose theory of paired electrons in polyatomic molecules, starting from the molecular orbitals, provided a general theory of electron correlation. The philosophy of this research on molecular orbital theory can be appreciated from a comment in the introduction to Part IX4 where reference is made to variational calculations on two-electron bonds: ’The most celebrated of such calculations were made by James & Coolidge (1933), who used elaborate wave functions with many parameters and succeeded in obtaining the energy of the two electrons in the hydrogen molecule to a high degree of accuracy. The disadvantage of these and similar calculations is that they do not bring out the major factors responsible for the stability of a chemical bond, nor do they lend themselves to generalization for other more complex molecules.” In addition to his research on molecular orbital theory, John Pople was active in statistical mechanics. His three papers under the general title of ‘Molecular Association in Liquids- exploited the concept of lonepair electrons to describe molecular interactions in polar liquids. His paper on the structure of water,’ involving the distortion of the hydrogen bonds, has proved to be of lasting value. His two papers on the statistical mechanics of assemblies of axially symmetry molecule^^^^^ gave us a general method of investigating the thermodynamic effects of angle-dependent intermolecular forces by treating the directional parts as a perturbation on the central-force interaction. My copies of these two papers are greatly soiled, for they formed the basis for my own work as John Pople’s first research student. (Alan Brickstock was also working under Pople’s supervision in 1953, but he was finishing off his work that started under the supervision of Lennard-Jones.) Pople’s contribution to the 1953 Faraday Discussion on “The Equilibrium Properties of Solutions of Non-Electrolytes” was devoted to the statistical mechanics of systems with noncentral (5) Hurley, A. C.; Leonard-Jones, Sir John; Pople, J. A. Proc. R. Soc. A 1953, 220,446455, (6) Lennard-Jones, Sir John; Pople, J . A. Proc. R . Soc. A 1951, 205, 155-162. (7) Pople, J. A. Proe. R . Soc. A 1951, 205, 163-178. (8) Pople, J. A. Proc. R . Soc. A 1952, 2 1 5 , 6 7 4 3 , (9) Pople, J. A. Proc. R. Soc. A 1954,221, 498-501. (10) Pople, J. A. Proc. R . Soc. A 1954, 221, 508-516.
Buckingham force fields.” His continuing interest in entropy first showed itself in print in his paper on “communal entropynI2which relates to the freedom of molecules in a liquid to move out of their “cells”. His major paper on semiempirical molecular orbital theory,I3 entitled “Electron interaction in unsaturated hydrocarbons”, was published in 1953, and in 1954 his short Note with R. K. NesbetI4 laid the foundation of UHF theory. Pople collaborated with Christopher Longuet-Higgins in research on the electronic spectra of aromatic molecules15J6and on solvent spectral shifts, presented at a memorable conference in Paris in 1957.” The paper by Pople and Longuet-Higgins on the theory of the Renner effect’* was stimulated by the spectroscopic work of Dressler and Ramsay on NH,; it remains a standard work on the subject. Nuclear magnetic resonance spectroscopy was emerging at this time as a major new chemical tool, and John Pople was quick to appreciate it. His papers on this topic formed a major part of the early issues of Mol. Phys., which started in 1958 under the editorship of Longuet-Higgins. His collaboration with W. G. Schneider and H. J. Bernstein of the National Research Council of Canada culminated in the publication of their masterly book19 in 1959. John Pople is a marvellously lucid expositor, thus greatly enhancing the impact of his research. He wrote a review of the molecular-orbital and equivalent-orbital approaches to molecular structure in 195720and on the theory of molecular structure and valence,21but the latter was written from the National Physical Laboratory in Teddington to which he went as Superintendent of the Basic Physics Division in 1958. This brings me to the end of my brief survey of John Pople’s Cambridge days. They were great times for theoretical chemistry. I was fortunate enough to experience the atmosphere but, above all, I had the extreme good fortune to have been one of John’s research students, and I am truly grateful. ( I 1) Pople, J. A. Discuss. Furuduy Soc. 1953, 15, 35-43. (12) Pople, J. A. Phllos. Mug. 1951, 42, 459-467. (13) Pople, J. A. Trans. Furuduy Soc. 1953,49, 1375-1385. (14) Pople, J. A.; Nesbet, R. K.J. Chem. Phys. 1954, 22, 571-572. (15) Pople, J. A. Proc. Phys. Soc. A 1955,68, 81-89. (16) Longuet-Higgins, H. C.; Pople, J. A. Proc. Phys. SOC.A 1955,68, 591-600. (17) Longuet-Higgins, H. C.; Pople, J. A. Colloq. Inr. CNRS 1959, 77, 337-343. (18) Pople, J. A.; Longuet-Higgins, H. C. Mol. Phy. 1958, 1 , 372-383. (19) Pople, J. A.; Schneider, W. G.; Bernstein, H. J. High-resolution Nuclear Mugnetic Resonance Spectroscopy; McGraw-Hill: New York, 1959; pp 501. (20) Pople, J. A. Q. Rev. (Chem. Soc. London) 1957, 11, 273-290. (21) Pople, J. A. Annu. Rev. Phys. Chem. 1959, 10, 331-348.
