levoisomer

A levoisomer is a specific type of stereoisomer. Stereoisomers are molecules that have the same chemical formula and the same sequence of bonded atoms, but differ in the three-dimensional arrangement of their atoms in space. The term "levo" comes from the Latin word "levo," meaning "left," and it refers to the direction in which the molecule rotates plane-polarized light. Specifically, a levoisomer rotates plane-polarized light to the left, or counterclockwise. This property is known as levorotation, and is denoted by the prefix "l-" or a minus sign (-) preceding the compound's name.

Levoisomers and dextroisomers are enantiomers of each other. Enantiomers are stereoisomers that are non-superimposable mirror images. If a molecule can exist as a levoisomer, it often also exists as its mirror image, a dextroisomer, which rotates plane-polarized light to the right (clockwise), denoted by "d-" or a plus sign (+). The terms levo and dextro are empirical observations and do not directly correlate with the absolute configuration (R/S designation) of a chiral center, which is determined by a more rigorous set of rules. However, for a given compound, if one enantiomer is levo, the other must be dextro, and vice versa, assuming they are enantiomers.

Many biologically active molecules, such as amino acids and sugars, exist as stereoisomers. The levo and dextro forms of these molecules can have vastly different biological effects. For example, one enantiomer might be a vital nutrient, while the other could be inactive or even toxic. Understanding and distinguishing between levoisomers and their counterparts is crucial in fields like pharmacology, biochemistry, and organic chemistry.