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Raman Optical Activity ROA

ROA is the differential response of a molecule to LCP vs. RCP radiation during a vibrational transition. It deals with chiral molecules, which means, as it was expressed by Lord Kelvin in 1884:

"I call any geometrical figure, or group of points, chiral, and say that it has chirality, if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself."

The measured ROA spectra of chiral molecules contain important information on their molecular geometries, e.g., conformations or structures.

Intensity of ROA
This tool is sensitive to the electric-electric, the electric-magnetic and the electric-quadrapole dipole moments, EDEDPD, EDMDPD and EDEQPD, respectively. In brief, the measured intensity of an ROA spectrum can be expressed by the Circular Intensity Difference CID:

δ = (I^R-I^L)/(I^R+I^L)

δ(0⁰)=0

δ(180º)=32β(G´)² / c[45α²+7β(α²)]

Skeletal chirality Conformation

• Secondary structure
• Loops
• turns