Dextrorotary

Dextrorotary

Dextrorotary, often abbreviated as "d-" or "(+)-", refers to the property of a chiral molecule that rotates plane-polarized light to the right, or clockwise, when viewed from the light source towards the observer. This optical activity is a key characteristic in stereochemistry, which is the study of the spatial arrangement of atoms in molecules and their effects on the physical and chemical properties of substances.

Optical Activity

Optical activity is a phenomenon observed in chiral compounds, which are molecules that cannot be superimposed on their mirror images. These molecules have at least one chiral center, typically a carbon atom with four different substituents. When plane-polarized light passes through a solution of a chiral compound, the plane of polarization is rotated. If the rotation is to the right, the compound is dextrorotary.

Measurement of Optical Rotation

The degree to which a compound rotates plane-polarized light is measured using a polarimeter. The observed rotation is expressed in degrees and can be either positive or negative. The specific rotation \( [\alpha] \) is calculated using the formula:

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

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

Importance in Chemistry and Pharmacology

The distinction between dextrorotary and levorotary (left-rotating) compounds is crucial in fields such as pharmacology and biochemistry. Enantiomers, which are pairs of molecules that are mirror images of each other, can have drastically different effects in biological systems. For example, one enantiomer of a drug may be therapeutically beneficial, while the other may be inactive or even harmful.

Examples of Dextrorotary Compounds

- Dextrose: Also known as D-glucose, this is a naturally occurring dextrorotary sugar that is a primary source of energy in living organisms. - Dextrorphan: An active metabolite of the cough suppressant dextromethorphan, which is dextrorotary and has different pharmacological effects compared to its levorotary counterpart.

Also see

- Levorotary - Chirality (chemistry) - Enantiomer - Polarimetry - Stereochemistry

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