Through twenty-five years of painstaking work, Norwegian physical chemist Odd Hassel confirmed the long-suspected three-dimensional nature of organic molecules, and his work in this field, called conformational analysis , altered the perception of chemistry. He received the Nobel Prize for chemistry in 1969, which he shared with the English chemist DerekH. R. Barton. Although other Norwegians had won the prize before him, Hassel's win was a special source of pride for his countrymen, for he was the first winner whose work had been carried out almost entirely in Norway.
One of a set of twins, Odd Hassel was born May 17, 1897, in Kristiana (now Oslo), Norway. His father Ernst was a gynecologist. His mother, Mathilde Klaveness Hassel, raised her four sons and one daughter alone after her husband died when Odd was eight years old. While his brothers, including his twin Lars, entered law and civil engineering, Hassel chose a different route. He had disliked school except for mathematics and science. The interest he developed in chemistry during high school evolved into his major area of study at the University of Oslo, which he entered in 1915.
Hassel toured France and Italy for a year after his graduation in 1920, a common practice at the time. In 1922 he worked at K. Fajans's laboratory in Munich where he discovered adsorption indicators, organic dyes used in the analysis of silver and halide ions for greater accuracy. He returned to school to study at the University of Berlin, a center for chemistry and physics, where he was recommended for and received a Rockefeller scholarship. He earned his doctorate in 1924.
While in Berlin, Hassel worked at the Kaiser Wilhelm Institute, and learned the technique known as X-ray crystallography. In this method of analysis the atomic structure of a substance can be determined by striking a pure crystal of the substance with X rays. After passing through the crystal, the rays are bent, or diffracted; the pattern of this diffraction is captured on photographic film and, when analyzed, reveals the arrangement of the atoms within the substance.
In 1925 Hassel returned to the University of Oslo as an instructor, and a year later was named associate professor of physical chemistry. In 1930 he began to investigate the three-dimensional structure of molecules, particularly ring-shaped carbon molecules . Many important organic molecules, including several carbohydrates and steroids, are built on a ring-shaped base. Although it was widely believed that all the carbon atoms in these molecules were arranged in one plane (rather like a doughnut lying on a plate), the possibility that they were actually three-dimensional had been proposed in 1885. Molecules having six or more carbon atoms, reasoned German chemist Johann Friedrich Wilhelm Adolf Baeyer, would be under too much strain to lie flat; in 1890 chemist Ulrich Sachse suggested two configurations of cyclohexane (a six atom carbon ring). One, the boat form, was represented as four atoms framing the "sides" laying in the same plane with the remaining atoms in the plane above them, like the bow and stern of a canoe. The second, or chair configuration, resembled a reclining shape having four atoms in the central plane, with one end atom above, and one below. In the absence of more conclusive experiments, however, most scientists maintained that cyclohexane resembled a doughnut on a plate.
Hassel's work was to correct that view. His primary investigations used the X-ray crystallography technique he had learned in Berlin; the drawback however, was that the technique could be used only with solids. A technique called dipole measurement, the analysis of positive and negative charges in a molecule, was also used. But electron diffraction proved to be the best method to investigate the structure of molecules because it could be used with gases and free molecules. By 1938 Hassel's laboratory was able to afford an electron diffraction unit, and he devoted the next five years to studying cyclohexane. Not only did he confirm that the boat and chair forms did indeed exist as predicted nearly fifty years before, Hassel also discovered that the molecules oscillated between the boat and chair forms at an enormous rate, with the latter form occurring predominantly. His investigations made it possible to predict the chemical properties of many organic substances whose base was cyclohexane. He also determined that the hydrogen atoms bonded to the carbon atoms either perpendicular to the four-atom plane (axial) or parallel (equatorial). These observations further deepened the behavioral chemistry of cyclohexanes and their related compounds--substituted cyclohexanes.
Hassel continued his work on cyclohexane even after Germany invaded Norway in 1940. He refused to publish his papers in German scientific journals, which limited the dissemination of his ideas. Some of his most important research was first reported in small Norwegian-language journals not circulated outside of Norway. In 1943, the Germans shut down the University of Oslo. Hassel, along with the other faculty members and scholars, was sent to a concentration camp at Grini, near Oslo. During his two years of imprisonment Hassel carried on his work, teaching physical chemistry without the consent of his captors. Despite his shy, reticent nature, he enlisted other scientists to work with him, including Per Andersen , and Ragnar Frisch, who remained a good friend and later received the Nobel Prize for economics the same year Hassel received one for chemistry. They were freed from Grini in November of 1944.
During the 1950s Hassel turned his attention to the physical structure of charge-transfer compounds . In such a compound, one part "donates" an electron to the other part, which "accepts" it. Because many of these compounds were too unstable to study in gaseous form, Hassel studied the solid forms with X-ray crystallography . He concluded that many of the theories about how these molecules worked were incorrect, and devised a new, simple set of rules that would inform the arrangement and size of the molecular bonds.
Hassel retired from the University of Oslo in 1964, but continued to research and publish until 1971. In the course of his career he published over 250 scientific papers, as well as Kristallchemie (1934), the first modern review of work in crystal chemistry. It was quickly translated into English, as Crystal Chemistry, and Russian. The book became a standard reference work for crystallographers and chemists throughout the field. From 1947 to 1957 Hassel was also the Norwegian editor of Acta Chimica Scandinavica. During his long career Hassel received numerous honors for his contributions to science. Apart from being honored with the Fridtjof Nansen Award in 1946, the Gunnerus Medal from the Royal Norwegian Academy of Sciences was awarded him in 1964, as well as the Guldber and Waage's Law of Mass Action Memorial from the Norwegian Chemical Society, of which he was an honorary fellow. In addition, he was a fellow of both the Royal Norwegian, and Royal Swedish Academies of Sciences, and Royal Danish Academy of Science. An honorary fellow of the British Chemical Society besides, Hassel received honorary degrees from the University of Copenhagen (1950) and the University of Stockholm (1960). He was made a knight of the Order of Saint Olav. In 1969, he shared the Nobel Prize for Chemistry with Derek Barton "for their contributions to the development of the concept of conformation and its application in chemistry." Speaking of the award to the New York Times, Hassel commented, "I had been among the chemistry candidates before, but did not expect to get the prize now. It was indeed very pleasing." He had doubts about going to Stockholm to accept the prize, however, saying, "I detest public appearances and have to think it over thoroughly." Hassel rarely attended international conferences and never married. "He prefers molecules," noted one of his students. After his twin brother died in 1980, Hassel reportedly lost his "zest for life." On May 15, 1981, Hassel died in Oslo, just two days before his eighty-fourth birthday.
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