![]() The "optical purity" is a comparison of the optical rotation of a pure sample of unknown stereochemistry versus the optical rotation of a sample of pure enantiomer. A pure enantiomer may be transformed into its racemate. A racemate may be separated into its component enantiomers. There are two ways in which the condition of a chiral substance may be changed:ġ. Chiral synthetic compounds, on the other hand, are commonly racemates, unless they have been prepared from enantiomerically pure starting materials. This is a result of the action of chiral catalysts we call enzymes, and reflects the inherently chiral nature of life itself. CH 3CH=CHCH 3 HBrĬhiral organic compounds isolated from living organisms are usually optically active, indicating that one of the enantiomers predominates (often it is the only isomer present). The addition of HBr to either cis- or trans-2-butene is an example of racemic product formation (the chiral center is colored red in the following equation). ![]() When chiral compounds are created from achiral compounds, the products are racemic unless a single enantiomer of a chiral co-reactant or catalyst is involved in the reaction. Such mixtures are called racemates or racemic modifications, and are designated (±). This isomer may be referred to as (–)-lactic acid or l-lactic acidĪ 50:50 mixture of enantiomers has no observable optical activity. This isomer may be referred to as ( )-lactic acid or d-lactic acid Lactic acid from muscle tissue: D = 2.5º This isomer may be referred to as (–)-carvone or l-carvone This isomer may be referred to as ( )-carvone or d-carvone For example, the lactic acid and carvone enantiomers discussed earlier have the following specific rotations. Specific rotations are useful in that they are experimentally determined constants that characterize and identify pure enantiomers. Each enantiomer of a stereoisomeric pair is optically active and has an equal but opposite-in-sign specific rotation. \(D\) designates that the light used is the 589 line from a sodium lampĬompounds that rotate the plane of polarized light are termed optically active.
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