Levorotary

Levorotary

In the field of chemistry and pharmacology, the term levorotary (also spelled laevorotary) refers to a property of certain chiral molecules that rotate plane-polarized light to the left, or counterclockwise, when viewed from the direction of the light source. This property is an important aspect of stereochemistry, which studies the spatial arrangement of atoms in molecules.

Properties

Chirality is a geometric property of some molecules and ions. A chiral molecule is non-superimposable on its mirror image, much like a person's left and right hands. Chiral molecules have at least one chiral center, typically a carbon atom with four different substituents.

Levorotary compounds are denoted by the prefix (−) or L-. This designation is based on the direction in which they rotate plane-polarized light. The opposite of levorotary is dextrorotary, which refers to compounds that rotate light to the right, or clockwise, and are denoted by the prefix (+) or D-.

Measurement

The degree to which a compound rotates plane-polarized light is measured using a device called a polarimeter. The specific rotation, denoted as \([\alpha]\), is calculated using the formula:

\[ [\alpha] = \frac{\alpha}{l \cdot c} \]

where: - \(\alpha\) is the observed rotation in degrees, - \(l\) is the path length of the sample cell in decimeters, - \(c\) is the concentration of the sample in grams per milliliter.

Biological Significance

In biological systems, chirality is crucial because most biomolecules are chiral. For example, amino acids, the building blocks of proteins, are almost exclusively L-amino acids in nature. Similarly, sugars are typically D-sugars. The chirality of these molecules affects their function and interaction with other biomolecules.

Applications

Levorotary compounds have significant applications in the pharmaceutical industry. Many drugs are chiral, and often only one enantiomer is therapeutically active. For instance, the drug thalidomide has one enantiomer that is effective as a sedative, while the other enantiomer is teratogenic.

Also see

• Chirality (chemistry)
• Dextrorotary
• Enantiomer
• Polarimetry
• Stereochemistry