IUPAC Atropisomers is defined as following A subclass of conformers which can be isolated as separate chemical species and which arise from restricted rotation about a single bond, e.g. ortho -substituted biphenyl, 1,1,2,2-tetra- tert -butylethane. The word atropisomer is derived from the Greek a , meaning not , and tropos , meaning turn . The name was coined by Kuhn in 1933, but atropisomerism was first detected in 6,6’-dinitro-2,2’-diphenic acid by Cristie in 1922. References: PAC, 1996, 68, 2193 (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2200 http://www.sciencemag.org/cgi/content/abstract/328/5983/1251 http://pubs.acs.org/doi/abs/10.1021/ja109165f http://pubs.acs.org/doi/abs/10.1021/ja109164t Wiki Article axial chirality