Cotton effect

Cotton effect

The Cotton effect is a phenomenon observed in the field of optical activity and chiroptical spectroscopy. It refers to the characteristic change in the circular dichroism (CD) spectrum of a chiral molecule near an absorption band. This effect is named after the British physicist A. Cotton, who first described it in 1895.

Description

The Cotton effect is observed as a positive or negative peak in the CD spectrum, which corresponds to the differential absorption of left and right circularly polarized light. This differential absorption is due to the interaction of the chiral molecule with the polarized light, leading to a difference in the extinction coefficients for the two polarizations.

Types of Cotton Effect

There are two types of Cotton effects:

• Positive Cotton effect: This occurs when the CD spectrum shows a positive peak at the absorption band.
• Negative Cotton effect: This occurs when the CD spectrum shows a negative peak at the absorption band.

Applications

The Cotton effect is widely used in the determination of the absolute configuration of chiral molecules. It is also employed in the study of protein and nucleic acid structures, as well as in the analysis of stereochemistry in organic compounds.

Related Concepts

• Circular dichroism
• Optical rotation
• Chirality (chemistry)
• Stereochemistry
• Chiral molecule

See Also

• Circular dichroism spectroscopy
• Optical rotatory dispersion
• Chiral analysis
• Enantiomer
• Diastereomer