Rotation, molecular optical

The reversion of gelatins to collagen has also been discussed with refer ence to cross-links. The denaturation of collagen results in marked changes of viscosity, optical rotation, molecular weight, volume, kinetics of proteolysis, and other properties. Under certain conditions a partial reversal of these changes can be achieved (Flory and Garrett, 1958 von Hippel... 

Table 2. Optical rotation, molecular formulae, molecular weight, FAB/MS and sulfate detection of saponins from B, rigidum...

Optical Rotation Molecular Weight Elemental Composition Appearance, Colour, Odour and Taste... 

The melting points, optical rotations, and uv spectral data for selected prostanoids are provided in Table 1. Additional physical properties for the primary PGs have been summarized in the Hterature and the physical methods have been reviewed (47). The molecular conformations of PGE2 and PGA have been determined in the soHd state by x-ray diffraction, and special H and nuclear magnetic resonance (nmr) spectral studies of several PGs have been reported (11,48—53). Mass spectral data have also been compiled (54) (see Mass spectrometry Spectroscopy). 

Polarimetric analysis of sorbitol and mannitol in the presence of each other and of sugars is possible because of their enhanced optical rotation when molybdate complexes are formed and the higher rotation of the mannitol molybdate complex under conditions of low acidity (194). The concentration of a pure solution of sorbitol may be determined by means of the refractometer (195). Mass spectra of trimethylsilyl ethers of sugar alcohols provide unambiguous identification of tetritols, pentitols, and hexitols and permit determination of molecular weight (196). 

Boiling-point at 9 mm. Specific gravity at 20° Optical rotation. Refractive index. Molecular refraction. ... 

Boiling-point Specific gravity. Refractive index Molecular refraction Optical rotation... 

Specific gravity Boiling-point. Optical rotation Refractive index Molecular refraction... 

Natural Occurrence of ( — )-proto-Quercitol. Although the dextrorotatory form (12) of proto-quercitol was discovered in acorns more than a century ago by Braconnot (5), who at first thought that it was lactose, the levorotatory form (13) remained unknown until 1961. In that year, Plouvier isolated it from leaves of the tree Eucalyptus populnea the yield was 0.55% (36). The optical rotation of the new compound was equal and opposite to that of the dextro enantiomer, and it was identical to the latter in its crystal form, melting point, solubilities, molecular formula and infrared spectrum. 

He is the author of two other books. Nonequilibrium Thermodynamics (1962) and Vector Analysis in Chemistry (1974), and has published research articles on the theory of optical rotation, statistical mechanical theory of transport processes, nonequilibrium thermodynamics, molecular quantum mechanics, theory of liquids, intermolecular forces, and surface phenomena. 

A classical, and still most useful, physicochemical parameter for characterizing glycosaminoglycans is their specific optical rotation. For pure heparins from common sources, [a]80 = + 45 to + 53 ° (see Table II). The actual value depends on the relative proportions of monosaccharide constituents (that is, the L-idosyluronic acid residues make a less positive contribution than the n-glucosyluronic residues), and on the degree of sulfation of the preparation (that is, although sulfate groups may have little direct influence on the molecular rotation, they lower the value by acting as diluents ). 

Because of their high molecular weight and their defined structure, dendrimers offer themselves for studying the expression of chirality on a macromolecular level. The construction of configurationally uniform macromolecules is otherwise a complex task but can be achieved more easily with dendrimers because of repetitive synthesis from identical (chiral) building blocks. Comparison of optical rotation values and circular dichroism (CD) spectra should demonstrate what influence there is of the chiral building blocks on the structure of the whole dendrimer. 

A unique chiral phosphine-phosphate ligand has been applied for hydrofor-mylation reaction of alkenes. In the case of 170 this ligand can be applied for obtaining poly(propylene-aZt-Co) with the highest molar optical rotation and with the highest molecular weight ([ ]d4 = + 40°, Mw = 104400, MJMn = 1.6) [284]. 

Within this historical setting, the actual birth of stereochemistry can be dated to independent publications by J. H. van t Hoff and J. A. Le Bel within a few months of each other in 1874. Both scientists suggested a three-dimensional orientation of atoms based on two central assumptions. They assumed that the four bonds attached to a carbon atom were oriented tetrahedrally and that there was a correlation between the spatial arrangement of the four bonds and the properties of molecules, van t Hoff and Le Bell proposed that the tetrahedral model for carbon was the cause of molecular dissymmetry and optical rotation. By arguing that optical activity in a substance was an indication of molecular chirality, they laid the foundation for the study of intramolecular and intermolecular chirality. 

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. 

Molecular asymmetry, chirality and enantiomers The observation of Louis Pasteur (1848) that crystals of certain compounds exist in the form of mirror Images laid the foundation of modem stereochemistry. He demonstrated that aqueous solutions of both types of crystals showed optical rotation, equal in magnitude (for solution of equal concentration) but opposite in direction. He believed that this difference in... 

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