atropisomers

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.
See: rotational barrier
Source:
PAC, 1996, 68, 2193 (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2200