The Nobel Prize in Chemistry 1976
Presentation Speech by Professor Gunnar
Hägg of the Royal
Academy of Sciences
Translation from the Swedish text
Your Majesties, Your Royal Highnesses,
Ladies and Gentlemen,
This year's Nobel Prize for Chemistry has been awarded to Professor William Lipscomb for his studies on the structure of boranes illuminating problems of chemical bonding.
A couple of days after the announcement of the chemistry Prize, a Swedish newspaper carried a cartoon by a wellknown Swedish cartoonist showing an elderly couple in front of their TV. The legend ran: "Can you remember ever having seen a borane, Gustav?" This question is quite proper, indeed. Gustav and his wife certainly had never seen a borane. Boranes do not exist in nature and can hardly be found in other places than chemical laboratories.
The name borane is the collective term for compounds of hydrogen with boron, the latter element forming part of among other things boric acid and borax. A great number of boranes and related compounds are known, and it is this whole group of substances which has been studied by Lipscomb. In the eighties of the last century it was understood that such compounds exist in the gas mixture that is formed when alloys between boron and certain metals are decomposed by acids. But it was only from about 1912 that the German chemist Alfred Stock succeeded in producing some pure boranes.
The structures and bonding conditions of boranes remained, however, unknown until about 1950, and it is not without reason that they have been considered problematical. The experimental study of the boranes has been very difficult. They are in most cases unstable and chemically aggressive and must, therefore, as a rule be investigated at very low temperatures. But it was still more serious that their structure and bonding conditions were essentially different from what was known for other compounds. Stock had found borane molecules that, for example, consisted of in one case two boron and six hydrogen atoms and in another case ten boron and fourteen hydrogen atoms. But when the object was to determine how these atoms are bound to each other, i.e. the appearance of the molecule, and also the nature of the bonds which keep the atoms together within the molecule, one was left in the dark for many years. One might suppose that these bonds were similar to those between the atoms in the hydrogen compounds of carbon, for instance in the hydrocarbons in liquefied petroleum gas. In these, the bond between two neighbouring atoms usually involves two electrons, an electron pair. However, boron does not have as many bonding electrons as carbon and, therefore, all the bonds cannot be of this type. A new type of bond, where two electrons co-operate in binding three atoms together, and which thus can master this electron deficiency, was proposed in 1949 but it was not until the researches of Lipscomb from 1954 and onwards that the problems of borane chemistry could begin to be solved satisfactorily.
Lipscomb has attacked these problems through skilful calculations of the possible combinations within the molecules of conceivable bond types and he has together with his collaborators determined the geometrical appearance of the molecules, above all using X-ray methods. But he has proceeded much farther than that in illuminating the binding conditions in detail through advanced theoretical computations. Thus it became possible to predict the stability of the molecules and their reactions under varying conditions. This has contributed to a marked development of preparative borane chemistry. These studies by Lipscomb have not only been applied to the proper, electrically neutral, borane molecules but also to charged molecules, i.e. ions, as well as other molecules related to the boranes.
It is rare that a single investigator builds up, almost from the beginning, the knowledge of a large subject field. William Lipscomb has achieved this. Through his theories and his experimental studies he has completely governed the vigorous growth which has characterized borane chemistry during the last two decades and which has given rise to a systematics of great importance for future development.
You have attacked in an exemplary way the very difficult problems within an earlier practically unknown field of chemistry. You have worked on a broad front using both experimental and theoretical methods and the success of your efforts is shown by the fact that your results and your views have governed the recent development of borane chemistry.
In recognition of your services to science the Royal Swedish Academy of Sciences decided to award you this year's Nobel Prize for Chemistry. To me has been granted the privilege of conveying to you the most hearty congratulations of the Academy and of requesting you to receive your prize from the hands of his Majesty the King.
From Nobel Lectures, Chemistry 1971-1980, Editor-in-Charge Tore Frängsmyr, Editor Sture ForsÚn, World Scientific Publishing Co., Singapore, 1993
Copyright © The Nobel Foundation 1976