Back in Oslo, Hassel originally focussed on inorganic chemistry, but beginning in 1930 his work concentrated on problems connected with molecular structure, particularly the structure of cyclohexane and its derivatives. He introduced the Norwegian scientific community to the concepts of the electric dipole moments and electron diffraction. After publishing a paper on the conformations of cyclohexane, Hassel was arrested by Norwegian Nazis and sent to the Griniconcentration camp until 1944.
Nobel Prize
Beginning in 1950, Hassel investigated the structure of charge-transfer compounds, and was eventually able to set up rules for the geometry of this kind of compound. He was awarded the Nobel Prize for chemistry in 1969, alongside Derek Barton.