axial chirality

Term used to refer to stereoisomerism resulting from the non-planar arrangement of four groups in pairs about a chirality axis. It is exemplified by allenesabC=C=Ccd (or abC=C=Cab) and by the atropisomerism of ortho-substituted biphenyls. The configuration in molecular entities possessing axial chirality is specified by the stereodescriptors R_a and S_a (or by P or M).