Britannica Sources used in this answer

Why do enantiomers usually have identical physical and chemical properties apart from optical rotation?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

Enantiomers are pairs of stereoisomers that are non-superimposable mirror images of each other, much like a pair of human hands.12

They possess identical physical properties—such as melting points, densities, and solubilities in achiral solvents—because the internal distances and forces between atoms within each individual molecule are the same. Similarly, their chemical properties are identical when they react with achiral reagents. This is because an achiral environment or reagent lacks the "handedness" required to distinguish between the two mirror-image structures; the interaction is analogous to a hand grasping a featureless ball, where both the left and right hands interact with the object in the exact same way.1324

Enantiomers only exhibit different behaviors when they interact with other chiral molecules or polarized light. In these chiral environments, the spatial arrangement of the enantiomers leads to distinct interactions, similar to how a right hand interacts differently with a labeled object than a left hand does. Consequently, their most notable difference is optical rotation, where they rotate the plane of polarized light in equal but opposite directions.1324