The word atropisomer (, , meaning "without turn") was coined in application to a theoretical concept by German biochemist Richard Kuhn for Karl Freudenbergs seminal Stereochemie' volume in 1933. Atropisomerism was first experimentally detected in a tetra substituted biphenyl, a diacid, by George Christie and James Kenner in 1922. Michinori Ōki further refined the definition of atropisomers taking into account the temperature-dependence associated with the interconversion of conformers, specifying that atropisomers interconvert with a half-life of at least 1000 seconds at a given temperature, corresponding to an energy barrier of 93 kJ mol (22 kcal mol ) at 300 K (27 °C).