Reference—Optical isomer drawing convention

Optical isomers have identical connectivity but opposite three-dimensional arrangements at a chiral centre. A solid wedge projects towards the viewer, a dashed wedge projects away, and ordinary bonds lie in the plane.

Keep the four attached group identities fixed, reflect the three-dimensional arrangement to draw the partner, and check that no rotation can superimpose the two structures.

For a tetrahedral carbon attached to H, OH, CH3 and CO2H, reverse the wedge/dash relationship to obtain the enantiomer without moving a group to a different atom.

A flat left-right redraw need not be a new optical isomer. If rotation makes the drawings coincide, they are two views of the same structure rather than an enantiomeric pair.