The Nobel Prize in Chemistry 1975

Vladimir Prelog

With an understanding of the tetrahedral nature of tetravalent carbon, organic compounds can be represented by a variety of structural drawings, as shown below. The stick, or Deriding, model shows the carbon at the center of the tetrahedron (dark gray) with the hydrogens at each vertex (light gray); the covalent radius of each atom is approximated by the size of the color band. The ball-and-stick model provides similar information and is sometimes easier to visualize, and the true Van derWalls radius of the atoms is best shown by the space-filling model (shown with a ball-and-stick overlay). More complex hydrocarbons containing carbon chains can be formed by creating additional carbon-carbon bonds, as shown below for chains containing two, four and six carbon atoms; you should note that in these structures, each carbon remains bonded to four other atoms (a valence of four). These molecules are also shown below in space-filling format: When viewing organic molecules it is important to note that the rotation around carbon-carbon single bonds is generally very rapid (greater than 106 rotations per second) and the chain can assume a large number of conformations (termed conformational isomers) which are rapidly interconverted and cannot be separated under normal circumstances. A sample of conformational isomers for four- and six-carbon chains are shown below: While drawings like those shown above most clearly show the structural features of organic molecules, it is clear that simpler methods are needed for routine representation of organic structures. The simplest, and least informative, is the simple representation of the molecular formula, showing ratios of atoms. A alternative format in which all atoms and all covalent bonds are shown is the "line-bond" or Kekul? structure. While this does provide information regarding bonding in the molecule, structures of this type are tedius to draw, and organic molecules are more commonly represented using some form of abbreviated "condensed structure". A further condensation of sturctural information is accomplished in "line" or "structural" drawings. In this format, each vertex in the drawing corresponds to a -CH2- group and each terminal line to a -CH3 group. It is assumed that all carbons have the appropriate number of hydrogens, and these are typically not shown. Multiple bonds are shown in structural drawings as double or triple lines, and it is again understood that the appropriate number of hydrogen atoms are attached. In actual practice, you will find organic structures represented by hybrids of all of these methods (as shown above); line structues to represent the backbone of a molecule, and some variation of condensed structures to show side-chains, or three-dimensional information, etc. As a student of organic chemistry, it is essential to learn to recognize these structural representations and to be able to interchange formats and to use these to visualize the full three-dimensional molecule in question. I was born on July 23rd, 1906 in Sarajevo in the province of Bosnia, which then belonged to the Austrian-Hungarian Monarchy and later, in 1918, became part of Yugoslavia. In the western world my birthplace has a somewhat sinister reputation that was characterized by an older tax-inspector in the Midwest of America as "the place where all that mess started". Actually, as an 8 years old boy I stood near to the spot where Archiduke Franz Ferdinand and his wife were assassinated. At the beginning of the first World War, in 1915, we moved to Zagreb, the capital of Croatia, where I attended the gymnasium. The period 1924 to 1929 was spent studying Chemistry at the Czech Institute of Technology in Prague, Czechoslovakia. The supervisor of my thesis was Professor Emil Votocek, one of the prominent founders of chemical research in Czechoslovakia. My mentor, however, was Rudolf Lukes, then lecturer and later successor of Votocek to the chair of organic chemistry. To Lukes I owe the greatest part of my early scientific education, and he remained my close friend until his premature death in 1960. In addition to these two "real" teachers I admired Robert Robinson, Christopher Ingold and Leopold Ruzicka, all of whom I considered as my "imaginary" teachers. In later years I was fortunate to become well acquainted with all three of these great chemists.

The close of my studies with a degree of a Dr. Ing. in 1929 coincided with the great economic crisis, and I was not able to find an academic position. I was therefore very grateful for a position in the newly created laboratory of G.J. Dr?za in Prague where rare chemicals were produced on small scale. I had there also a modest opportunity to do some research, but I badly wanted to work in an academic environment. This is why I was so eager to accept the position of a lecturer at the University of Zagreb in 1935. I did not know that I had to fulfil there all the duties of a full professor and to live on a salary of an underpaid assistant, but it would probably not have affected my decision if I had known. With the help of a couple of enthusiastic young co-workers and of a developing small pharmaceutical factory, I had just managed to solve at least the most urgent problems for myself and my laboratory when the second World War broke out. After the German occupation of Zagreb in 1941 it became clear that I was likely to get into serious trouble if I remained there. At this critical point I received an invitation of Richard Kuhn to give some lectures in Germany, and shortly afterwards Leopold Ruzicka, whom I had asked for help, invited me to visit him on the way. With these two invitations, it was possible for me to escape with my wife to Switzerland. Through Ruzicka I soon obtained generous support of CIBA Ltd. and started work in the Organic Chemistry Laboratory at the Federal Institute of Technology (ETH) in Zurich. The cooperation with Ruzicka lasted many years and enabled me to make my slow progress up the academic hierarchical ladder. Starting as assistant, I became "Privat Dozent", "Titularprofessor" associate (ausserordentlicher) professor and in 1952 full professor ad personam. Finally, in 1957, I succeeded Ruzicka as head of the Laboratory, a height that I never dreamt of when I was a student in Prague. In becoming director of the Laboratory I reached, according to Peter's principle, the level of my incompetence and I tried hard for several years to step down. Surrounded and supported by a group of very able young colleagues, I finally succeeded in introducing a rotating chairmanship from which I was exempted. So far this has worked very satisfactorily and it may have helped some of my colleagues to resist tempting offers from other Universities.

My main interests were natural compounds, from adamantane and aialoids to rifamycins and boromycin. During the work on natural compounds stereochemical problems emerged from all sides. As E.L. Eliel pointed out, stereochemistry is not so much a branch of chemistry but rather a way of looking at chemistry. It was, and still is, great fun trying to find new points of view for it.

I travel a lot. Recently I counted that I have given lectures in more than 150 places, often several times. This in spite of the fact that I do not speak any language properly. I suspect that many people come to my lectures because they enjoy my strange accent and skill in managing without actually cheating.

I married my wife Kamila in Prague in 1933. A son Jan was born to us in Z?rich in 1949.

For many years, when still a Yugoslav citizen, I was already a Swiss patriot and in 1959 I obtained Swiss citizenship. However, I consider myself a world citizen and I am very grateful to my adopted country that it allows me to be one.

The way from Sarajevo to Stockholm is a long one and I am fully aware that I have been very lucky to arrive there. The journey could not have been made without the generous help of friends, colleagues, co-workers and also of innumerable earlier chemists "on whose shoulders we stand".

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