Levorotatory
Definition and meaning of Levorotatory in chemistry.
Levorotatory refers to a compound or solution that rotates the plane of polarized light counterclockwise (to the left) when viewed toward the light source. This optical activity is designated with a minus sign (−) or the notation (l) in chemical nomenclature.
In more detail
Optical rotation occurs when a compound contains a chiral center and is optically active. The magnitude and direction of rotation depend on the molecular structure, wavelength of light, solvent, and concentration. Levorotatory substances are often paired with dextrorotatory enantiomers that rotate light in the opposite direction. Importantly, the direction of rotation is independent of the D/L stereochemical configuration, which is based on atomic priorities at the chiral center rather than actual rotational direction.
Key facts
| Field | Physical Chemistry |
|---|---|
| Optical Designation | (−) or (l) |
| Measurement Tool | Polarimeter |
| Opposite Property | Dextrorotatory |
(−)-Menthol (C10H20O), the naturally occurring form of menthol found in peppermint oil, is levorotatory and rotates plane-polarized light counterclockwise.
Frequently asked questions
Is levorotatory the same as an L-configured molecule?
No. The (−) or (l) notation describes the actual direction of optical rotation, while L describes absolute stereochemical configuration at the chiral center. These properties are independent and cannot be predicted from one another. For example, L-(+)-lactic acid (produced in muscle tissue during exercise) is dextrorotatory, not levorotatory.
How is levorotatory activity measured?
Using a polarimeter, which measures the angle through which plane-polarized light is rotated when passing through the optically active solution.