Optical rotation example

An example of a chiral compound is lactic acid. Two different forms of lactic acid that are mirror images of each other can be defined (Figure 2-69). These two different molecules are called enantiomers. They can be separated, isolated, and characterized experimentally. They are different chemical entities, and some of their properties arc different (c.g., their optical rotation),... 

Any property of a reacting system that changes regularly as the reaction proceeds can be formulated as a rate equation which should be convertible to the fundamental form in terms of concentration, Eq. (7-4). Examples are the rates of change of electrical conductivity, of pH, or of optical rotation. The most common other variables are partial pressure p and mole fraction Ni. The relations between these units... 

Linalol is not particularly easy to purify, as it yields practically no crystalline compounds suitable for purification purposes. The characters of the various specimens prepared therefore vary, especially in regard to their optical rotation. The following figures, for example, have been recorded for linalol with a laevo-rotation —... 

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. 

Without going into too much detail, it is relatively easy to intuitively understand optical rotation in second-harmonic generation from a chiral thin film by simply considering the nonvanishing polarization components generated in a chiral and achiral film. For example, for an achiral thin film with CXA, symmetry and for the experimental situation shown in Figure 9.5, the nonvanishing components of the polarization can be written as ... 

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 chemical interrelation method for determining the absolute configuration of a compound involves the conversion of this compound to a compound with a known configuration, and then the absolute configuration is deduced from the resulting physical properties, such as optical rotation or GC behavior. An example is shown in Scheme 1-12. 

How conformation is related with optical rotation is brought out by the fact that with decreasing temperature there is an increase of rotation of conformationally mobile compounds. This is explained that at ordinary temperatures, several conformations occur at equilibrium, the rotation of which may be opposite in sign and so the total rotation is small. With the decreasing temperature the equilibrium is displaced in favour of the most preferred conformation with a characteristic rotation. An example of this is butanol-2. 

Some compounds exhibit the property of being able to rotate the plane of polarized light. In other words, when a beam of plane-polarized light passes through a sample of such a compound, the plane is rotated to another position around the fine of travel (Figure 15.13(c)). The property is called optical rotation, or optical activity. In order to be optically active, a compound must possess an asymmetric carbon atom in its molecular structure. An asymmetric carbon atom is one that has four different structural groups attached to it. An example of such a compound is 2-butanol ... 

Activity in the field was, however, expanding. For example, in 1927 Drew and Haworth (65) obtaind a crystalline polymeric powder by the action of hydrogen chloride on the lactone of 2,3,4-trimethyl-l-arabonic acid. Citing the increase in melting point and molecular weight, and loss of specific optical rotation, they ascribed a cyclic, high polymer structure to this polyester. 

A wide range of physical constants, for instance melting point, boiling point, specific gravity, viscosity, refractive index, solubility, polymorphic forms vis-a-vis particle size, in addition to characteristic absorption features and optical rotation play a vital role in characterization of pharmaceutical chemicals and drug substances. These physical constants will be discussed briefly with typical examples as under ... 

Part—IV has been entirely devoted to various Optical Methods that find their legitimate recognition in the arsenal of pharmaceutical analytical techniques and have been spread over nine chapters. Refractometry (Chapter 18) deals with refractive index, refractivity, critical micelle concentration (CMC) of various important substances. Polarimetry (Chapter 19) describes optical rotation and specific optical rotation of important pharmaceutical substances. Nephelometry and turbidimetry (Chapter 20) have been treated with sufficient detail with typical examples of chloroetracyclin, sulphate and phosphate ions. Ultraviolet and absorption spectrophotometry (Chapter 21) have been discussed with adequate depth and with regard to various vital theoretical considerations, single-beam and double-beam spectrophotometers besides typical examples amoxycillin trihydrate, folic acid, glyceryl trinitrate tablets and stilbosterol. Infrared spectrophotometry (IR) (Chapter 22) essentially deals with a brief introduction of group-frequency... 

In 1974 the first example of asymmetric induction in an intramolecular Pummerer reaction was observed and reported. Stridsberg and AUenmark (300) treated optically pure o-benzylsulfinylbenzoic acid 271 with acetic anhydride in the presence of dicyclohexyl-carbodiimide (DCC) and found that the Pummerer reaction product, 3,l-benzoxathian-4-one 272, was optically active. The sign and optical rotation values ([alp varied from +42° to -11°) of 272... 

A special mention in the field of enantioselective HPLC separations must be made of chiro-optical detection systems, such as circular dichroism (CD) and optical rotation (OR), which can be also used to circumvent the low UV detectability of chromophore-lacking samples [40, 61]. While sensitivity of chiro-optical detection is not always sufficient to perform enantiomeric trace analysis, the stereochemical information contained in the bisignate spectropolarimetric response is useful in establishing elution order for those compounds not available as single enantiomers of known configuration. An example of application of different online detection systems (UV and CD at 254 nm) in the enantioselective separation of a racemic sulfoxide on a commercially available TAG CSP is reported in Figure 2.12, under NP conditions. 

For a number of optically active ions of the type cis-M(AA)2XY, where M = Co and Cr, there is an initial optical rotation change (mutarotation) that is similar in rate to that of acid hydrolysis, for example,... 

A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer. Such a mixture is known as racemic mixture or racemic modification. A racemic mixture is represented by prefixing dl or (+) before the name, for example ( ) butan-2-ol. The process of conversion of enantiomer into a racemic mixture is known as racemisation. 

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