Angle of optical rotation

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. 

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°. 

First item in a series (for example, the first carbon linked to a carboxyl group). 2. Abbreviation for alpha particle. 3. Symbol for angle of optical rotation. 4. Symbol for degree of dissociation. 5. Symbol for electric polarizability of a molecule. 6. Often with a subscript number (i) the coefficient of [A] in the numerator of the generalized rate expression. 7. Symbol for is proportional to. 8. Symbol for Napierian absorption coefficient. 9. In brackets, symbol for specific optical rotation. 

For the unequivocal characterization of a low-molecular-weight compound, it is sufficient to specify a few physical or chemical properties, for example, boiling point, melting point, angle of optical rotation, refractive index, elemental analysis, IR and NMR spectra. If two low-molecular-weight samples have the same characteristic properties, they may be considered as identical. 

Angle of optical rotation a Dalton (atomic mass unit) Da... 

Circular Dichrograph. An instrument similar to a specliopolaiimeter. Instead of a change in angle of optical rotation versus wavelength, the instrument records the difference in dichroic absorption versus wavelength,... 

NAME Absorbance Absorption factor Angle of optical rotation Angular frequency Emissivity, emittance Frequency... 

Thermal-expansion coefficient, degree of dissociation, polarizability, angle of optical rotation, adjustable parameter (least squares)... 

Figure 22.14 Operation of a polarimeter. Initially, the tube is filled with an achiral compound. The analyzer Is rotated so that its plane of polarization is perpendicular to that of the polarizer. Under this condition, no light reaches the observer. Next, a chiral compound Is placed In the tube as shown. The plane of polarization of the polarized light is rotated as It travels through the tube so that some light reaches the observer. Rotating the analyzer (either to the left or to the right) until no light reaches the observer again enables the angle of optical rotation to be measured.

Specific optical rotation for the sodium D line at 25 °C, as denoted by In stereochemistry, the specific rotation of a chemical compound [a] is defined as the observed angle of optical rotation a when plane-polarized light is passed through a sample with a path length of 1 decimetre and a sample concentration of 1 gram per 1 millilitre. 

A diamond anvil cell can also serve as an optical high pressure cell [14]. Transitions between liquid crystalline phases which exhibit optical activity can be indicated by jumps in the angle of optical rotation [15]. 

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