OpenSMILES uses @ and @@ to denote tetrahedral chirality. In some cases not all vertices of a tetrahedron correspond to atoms, but rather to lone pairs. The v1.0 of the specification does not specify whether OpenSMILES supports such chiralities or not.
I think OpenSMILES could support that by saying that if one vertex of a tetrahedron is lone pair, then it is considered to be the first atom in the clockwise or anticlockwise accounting. If both lone pair and implicit hydrogen is present, then the order is first lone pair, then hydrogen. These suggestions are of course arbitrary and could be modified to he liking of OpenSMILES authors.
OpenSMILES uses
@and@@to denote tetrahedral chirality. In some cases not all vertices of a tetrahedron correspond to atoms, but rather to lone pairs. The v1.0 of the specification does not specify whether OpenSMILES supports such chiralities or not.I think OpenSMILES could support that by saying that if one vertex of a tetrahedron is lone pair, then it is considered to be the first atom in the clockwise or anticlockwise accounting. If both lone pair and implicit hydrogen is present, then the order is first lone pair, then hydrogen. These suggestions are of course arbitrary and could be modified to he liking of OpenSMILES authors.