Enantiomers

Definition

Enantiomers are a pair of stereoisomers that are non-superimposable mirror images of each other. They have the same molecular formula and connectivity, but differ in the spatial arrangement of their atoms, resulting in a unique handedness or chirality.

5 Must Know Facts For Your Next Test

1. Enantiomers have the same physical and chemical properties, except for their ability to rotate plane-polarized light in opposite directions.
2. The presence of a tetrahedral carbon atom with four different substituents is a key structural feature that gives rise to chirality and enantiomers.
3. Pasteur's discovery of enantiomers through the separation of tartaric acid crystals was a significant milestone in the understanding of molecular chirality.
4. The Cahn-Ingold-Prelog sequence rules provide a systematic way to specify the absolute configuration of chiral molecules.
5. Enantiomers can have drastically different biological effects, as they interact differently with chiral receptors and enzymes in living organisms.

Review Questions

• Explain the relationship between enantiomers and the tetrahedral carbon atom.
  • The presence of a tetrahedral carbon atom with four different substituents is a key structural feature that gives rise to chirality and the formation of enantiomers. The tetrahedral arrangement of the four substituents around the carbon atom results in a non-superimposable mirror image pair, which are the enantiomers. This unique spatial arrangement of atoms is what confers the characteristic handedness or chirality to the molecule.
• Describe how Pasteur's discovery of enantiomers led to the understanding of molecular chirality.
  • Pasteur's groundbreaking work on the separation of tartaric acid crystals was a pivotal moment in the discovery of enantiomers and the understanding of molecular chirality. By manually separating the left-handed and right-handed crystals, Pasteur demonstrated that these two forms of tartaric acid had the same chemical composition but differed in their ability to rotate plane-polarized light in opposite directions. This observation was a crucial step in establishing the concept of chirality, where molecules can exist as non-superimposable mirror images, leading to the further development of sequence rules for specifying the absolute configuration of chiral molecules.
• Discuss the significance of enantiomers in biological systems and chiral environments.
  • Enantiomers are of great importance in biological systems and chiral environments because they can have dramatically different biological effects. Due to the inherent chirality of many biological molecules, such as enzymes and receptors, enantiomers interact with these chiral entities in unique ways. One enantiomer may be pharmacologically active and beneficial, while the other may be inactive or even have adverse effects. This property of enantiomers is crucial in the development of pharmaceuticals, where the desired enantiomer must be selectively synthesized or separated to ensure the intended therapeutic effect. Additionally, the presence of chiral environments in nature, such as those found in living organisms, can lead to the preferential formation or accumulation of specific enantiomers, which is observed in the configurations of many biomolecules, including amino acids and carbohydrates.

Related terms

Chirality:

The property of a molecule that is non-superimposable on its mirror image, meaning it has a unique handedness or 3D arrangement of atoms.

Optical Activity:

The ability of a chiral molecule to rotate the plane of polarized light, either clockwise (dextrorotatory) or counterclockwise (levorotatory).

Meso Compounds:

Achiral molecules that have both a plane of symmetry and a center of symmetry, resulting in the cancellation of optical activity.