Circular dichroism - Ennisokusei

Also known as circular dichroism, or CD. This is the phenomenon in which an optically active substance absorbs circularly polarized light differently for left-handed and right-handed circularly polarized light. If the absorption of left-handed and right-handed circularly polarized light differs, the circularly polarized light that passes through the substance becomes elliptically polarized. Circular dichroism is expressed with the molecular ellipticity [θ] on the vertical axis and the wavelength (nm) on the horizontal axis. If the relative ellipticity of [θ] is [ψ], then

[θ]＝[ψ]×molecular weight×10 ⁻² = 3300( ε _l − ε _r )

Here, ε _l and ε _r are the molar extinction coefficients for left- and right-handed circularly polarized light. [ψ] is the ellipticity of a solution (density: ρ) containing c g of active solute in 100 mL of l dm of liquid layer, where ψ is the ellipticity of the solution.

[ψ] = ψ/ lc ρ
In the diagram, the maxima in the positive region are called circular dichroism maxima, and the minima are called circular dichroism minima. On the other hand, the maxima in the negative region are called negative circular dichroism minima, and the minima are called negative circular dichroism maxima. Circular dichroism curves are closely related to optical rotatory dispersion curves and electronic spectra (absorption spectra). The maximum wavelength of the circular dichroism curve is approximately equal to the midpoint of the wavelengths between the peak and valley of the optical rotatory dispersion curve, and also coincides with the maximum wavelength of the absorption spectrum. Circular dichroism can only be observed in substances that have an asymmetric center within the molecule.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

円偏光二色性，CDともいう．旋光性物質の円偏光に対する吸収が，左円偏光と右円偏光とで異なる現象．左まわりの円偏光と右まわりの円偏光に対する吸収が異なれば，この物質を通過した円偏光はだ円偏光になる．円二色性は縦軸に分子だ円率[θ]，横軸に波長(nm)をとって表示される．[θ]は，比だ円率を[ψ]とすると，

[θ]＝[ψ]×分子量×10^－2 ＝ 3300(ε_l － ε_r)

で表される．ここで，ε_l および ε_r は左および右円偏光のモル吸光係数である．また[ψ]は，100 mL 中にcg の活性溶質が含まれている溶液(密度：ρ)のl dm の液層に対するだ円率をψとして，

[ψ] ＝ ψ/lcρ
で表される．図において，正の領域内にある極大を円二色性極大，極小を円二色性極小とよぶ．一方，負の領域にある極大を負の円二色性極小，極小を負の円二色性極大という．円二色性曲線は，旋光分散曲線や電子スペクトル(吸収スペクトル)と密接な関係を有する．円二色性曲線の極大波長は，旋光分散曲線の山と谷の波長の中点にほぼ等しく，また吸収スペクトルの極大波長と一致する．円二色性は分子内に不斉中心をもつ物質に限って観測される．

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