Rotatory power, determination

Rotatory power, determination of, 504 Rubber, natural unvulcanised, 1022 synthetic, 1022 Rubber stoppers, 55 boring of, 56... 

Determination of Rotatory Power. —The 1 otatory p o < 1 of ethyl tartiate, which is an optically active substance, is determined by means of a polarimetcr. One of these insti U-ments known as Laurent s polarimeter is shown in l- igs. 71 and 72. 

The following discussion is divided into three subsections the ketone chromophore (Section 4.4,1.1.), for which configurational assignments are based on the effect of ring dissymmetry and substitution pattern on the rotatory power of the n-rt transition. For conjugated chro-mophores (Section 4.4.1.2.) it is both the helicity of the chromophore and the vicinal substituent effect that determines the rotatory power of the 71-71 transition. Finally, the versatile stereochemical method, exciton chirality method (Section 4.4.2.), is based on the chiral interaction between the electric dipoles of the allowed transitions in two or more chromophores. 

Methyl 2,4-dimethylhexanoate (diastereoisomeric mixture) was 16.6% of the original mixture. Methyl 4-methylheptanoate 3.2% of the original mixture was recovered in such a small quantity that its optical rotatory power could not be determined. 

Fundamental Principles.—The determination of two or more sugars present in a mixture is usually carried out by indirect methods, based on (1) the rotatory powers, (2) the reducing powers,and (3) the transformation of certain sugars into others by inversion, which is effected by dilute acids or special enzymes. From the rotatory and reducing powers of the mixture, in some cases both before and after inversion, the quantity of each sugar in the mixture is calculated. 

This is obtained from the peel of the fruit of Citrus aurantium (var. dulcis) and is a golden-yellow liquid with an odour of oranges and a sweetish, aromatic taste. It contains limonene (about 90%), linalool, terpineol, nonyl alcohol, decyl aldehyde and esterified caprylic acid. If adulterated with bitter orange cal (q.v.), the latter is detectable by determinations of the sp. gr. at 15°, rotatory power and residue on evaporation (see Oil of Lemon) and by fractional distillation. 

External Characters Specific Gravity Rotatory Power Solubility in 90% and 80% Alcohol.—These determinations are made as described under General Methods. 

Fractional Distillation (Romeo and Moricca s method).—30 c.c. of the oil are distilled either under reduced pressure (20-30 mm.) in an oil-bath or at ordinary pressure by direct heating, two fractions of exactly 5 c.c. each being collected. The rotatory power (at 15-20°) of the distilled fractions and of the residue are determined and referred to a tube 10 cm. long. 

Estimation of Catalytic Activity. The catalytic activities of the copolymers on the hydrolysis of polysaccharides were estimated, with the measurement of increase in reducing sugar in the reaction mixture with reaction time according to Somogyi method (22). The hydrolysis rates of sucrose were determined from the measurement of optical rotatory power... 

Some of these topics have been elaborated in Section 1.2, where the reader is referred to the many excellent monographs and articles which are available, and which fully explore the current aspects of the stereochemistry of molecules and the importance of stereochemical considerations of appropriate reaction processes. This section is devoted to the experimental determination of optical rotatory power. 

Quantitative conclusions regarding the reduction of optical rotatory power of these derivatives by the increased distance of the pairwise interactions must, of course, await optical purity determinations. Qualitatively, however, expectations are obviously confirmed 179 ... 

The two diastereoisomers do not differ greatly in solubility. A prolonged systematic fractionation is then required, and usually only the less soluble salt is obtained pure. The course of the separation is followed generally by determining the rotatory power of the various fractions and by observing the changes in solubility and crystalline appearance of the successive fractions. 

Liquid oxygen is a non-conduetor of electricity but it is strongly attracted by a magnet.5 It readily absorbs nitrogen from the atmosphere, and can be mixed with liquid fluorine without suffering chemical change. The magnetic rotatory power and dispersion have been determined.6... 

The measured crystal optical activity, in general, can be either of molecular origin or due to the chiral helical arrangement of chiral or achiral molecules in the crystal, or both. The two factors are difficult to separate. Kobayashi defined a chirality factor r = (pc — ps)/pc = 1 — pslpc, where pc is the rotatory power per molecule of a randomly oriented crystal aggregate derived from the gyration tensors determined by HAUP, and ps that in solution [51]. It is a measure of the 4 crystal lattice structural contribution to the optical activity and represents the severity of the crystal lattice structural contribution to the optical activity, and represents the severity of the restriction of the freedom of molecular orientation by forming a crystal lattice. Quartz is a typical example of r = 1, as it does not contain chiral molecules or ions and its optical activity vanishes in random orientation (ps = 0). 

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