Final answer:
Two molecules are enantiomers if they are nonsuperimposable mirror images with chiral centers, differing only in how they affect plane-polarized light and interact with other chiral substances.
Step-by-step explanation:
Identifying Enantiomers Based on Chirality
To determine if two molecules are enantiomers, we must examine their chirality. Chiral molecules are nonsuperimposable mirror images of each other, much like the relationship between left and right-handed gloves. A key factor in identifying enantiomers is that, despite having nearly identical physical and chemical properties, they differ in the way they interact with plane-polarized light. One will rotate the light clockwise, known as dextrorotatory (d or (+)), and the other counterclockwise, termed levorotatory (l or (-)). Additionally, because of the way enantiomers interact with other chiral substances, such as enzymes in biological systems, they can show different biological activities.
An important characteristic of chiral molecules is the absence of a plane of symmetry, leading to two molecules that are mirror images but cannot be superimposed on each other, meaning they cannot be made to match exactly no matter how they are rotated or arranged in space.
Chirality is crucial in many biologically active molecules, such as in the case of glucose and amino acids like alanine, where the two enantiomeric forms can have vastly different effects in biological systems. This difference is vital in drug development, as only one enantiomer may be therapeutically active and the other may be inactive or cause adverse effects.