Born May 17, 1897, in Oslo. Norwegian physical chemist. Member of the Norwegian Academy of Sciences in Oslo (1933).

Hassel graduated from the University of Oslo in 1920. Between 1921 and 1925 he continued his studies at universities in France, Italy, and Germany, receiving the Ph.D. degree in 1924. In 1926 he became a docent, and in 1934, a professor, at the University of Oslo, where he remained until 1964.

Hassel is one of the founders of conformational analysis and the author of many basic works on stereochemistry and crystal chemistry. He was the first to make use of X rays in the study of cyclohexane and showed that its six-member ring has a chair conformation; he later demonstrated that this conformation is also found in cyclohexane derivatives, which are systems containing fused cyclohexane rings, as well as in certain sugars, such as pyranoses. He proposed the nomenclature and designations of substituents in various positions in the ring.

Hassel shared a Nobel Prize in 1969 with the British chemist D. Barton.