Optical rotation angle

R.K. Kondru et al., Atomic contributions to the optical rotation angle as a quantitative probe of molecular chirality. Science 282, 2247-2250 (1998)... 

R.K. Kondru et al., Structural and conformational dependence of optical rotation angles. J. Phys. Chem. A 103, 6603-6611 (1999)... 

FIGURE 17.1 Plot of the specific optical rotation angle as a polynomial of the QS Euclidian... 

The angle of rotation is, of course, directly proportional to the thickness of the layer of active substance through which the polarised light passes. The expression optical rotation or rotatory power is universally understood to be the observed angle of rotation produced by a column of 100 mm. of the optically active substance. If tubes of other lengths be... 

Instrumental methods have largely supplanted direct analysis. Any property directly proportional to concentration can be used, such as the angle of optical rotation, the absorbance at a fixed wavelength, or the area of an NMR peak. 

Racemization constitutes a special case of opposing first-order reactions. The equilibrium constant is unity, and the opposing rate constants are equal to one another. Racemization can be followed by polarimetry (monitoring the angle of optical rotation) or by circular dichroism (monitoring the ellipticity). The kinetic analysis can be done by either Eq. (3-15) or (3-16). The rate constant for racemization is krac = ke/2. 

The determination of the angle of rotation is called polarimetry. In some cases, it can help a chemist follow a reaction. For example, if a reaction destroys the chirality of a complex, then the angle of optical rotation decreases with time as the concentration of the complex falls. 

Marvel, Dec, and Cooke [J. Am. Chem. Soc., 62 (3499), 1940] have used optical rotation measurements to study the kinetics of the polymerization of certain optically active vinyl esters. The change in rotation during the polymerization may be used to determine the reaction order and reaction rate constant. The specific rotation angle in dioxane solution is a linear combination of the contributions of the monomer and of the polymerized mer units. The optical rotation due to each mer unit in the polymer chain is independent of the chain length. The following values of the optical rotation were recorded as a function of time for the polymerization of d-s-butyl a-chloroacrylate... 

Optical rotation. When test is carried out as directed in general method (2.2.7), the angle of optical rotation of solution S is —0.10° to +0.10°. 

If polarized light passes through a medium that exhibits optical rotation, the motion along one of the circular vectors is slower than that of the other. The resultant vector is thus displaced from the original vector by some angle, . Figure 16.5 shows the vector model in which the phase difference is [Pg.588]

Figure 9.2 Quantitative description of optical rotation. A vertically polarized electric field Em is incident on chiral system and induces vertically directed dipole moment i and magnetic moment m. Both act as sources of radiation, p, giving rise to vertically polarized field, m giving rise to horizontally polarized field. Sum of both fields is a new field E0ut with polarization rotated over angle 0.

This effect, which is in a loose sense the nonlinear analog of linear optical rotation, is based on using linearly polarized fundamental light and measuring the direction of the major axis of the ellipse that describes the state of polarization of the second-harmonic light. For a simple description of the effect, we assume that the expansion coefficients are real, as would be the case for nonresonant excitation within the electric dipole approximation.22 In this case, the second-harmonic light will also be linearly polarized in a direction characterized by the angle... 

We anticipate that, regardless of the detuning from an optical resonance used, the parameters f, g, and h will always be determinable from measurements of SHG as a function of the rotation angle of a quarter waveplate used to set the polarization state of the incident fundamental light. The amount of SHG-CD can be calculated from the parameters or, of course, read directly... 

The symmetry of the LB films was determined by polarized ultraviolet-visible (UV-Vis) absorption spectroscopy, optical rotation, and second-harmonic generation. All studies showed that the constructed LB films are anisotropic in the plane of the film and that the symmetry of the film is C2 with the twofold rotation axis perpendicular to the film plane. For example, when the SH intensity is plotted as a function of the azimuthal rotation angle (rotation around an axis perpendicular to the plane of the film), the twofold symmetry becomes evident (Figure 9.23). Isotropic films generate an SH signal independent of the azimuthal rotation angle. On the other hand, the LB... 

The optical rotation of a number of pure pharmaceutical substances may be measured accurately by noting the angle through which the plane of polarization is rotated when polarized light passes through the substance, if liquid or through a solution of the substance, if solid. 

The specific optical rotation of a solid substance is usually determined by measuring the angle of rotation at the wavelength of the sodium D-line at a temperature of 20°C, and calculating the result with reference to a layer 1 dm thick of a solution containing 1 g of the substance per ml. It is pertinent to mention here that the specific optical rotation of a solid is always expressed to a given solvent and concentration. 

Procedure Determine the angle of rotation of the freshly prepared 4% w/v solution of adrenaline in 1 M hydrochloric acid with the help of a previously checked polarimeter. The mean value of at least five similar determinations is employed in the calculation of the specific optical rotation. 

It should first be noted that the measurement of emission anisotropy is difficult, and instrumental artefacts such as large cone angles of the incident and/or observation beams, imperfect or misaligned polarizers, re-absorption of fluorescence, optical rotation, birefringence, etc., might be partly responsible for the difference between the fundamental and limiting anisotropies. 

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