Dextrorotatory substances

In the laboratory, we can measure a rotation and see whether a particular substance is (+) or (-). On paper, we can determine whether a particular drawing is named (R) or (5). But it is difficult to predict whether a structure we call (R) will rotate polarized light clockwise or counterclockwise. Similarly, it is difficult to predict whether a dextrorotatory substance in a flask has the (R) or (S) configuration. 

The direction of rotation of the polarization plane depends on the substance if the plane of polarization turns clockwise in relation to k, the substance is referred to as a right-hand (or dextrorotatory) if it turns anticlockwise, the substance is a left-hand (or laevorotatory) substance. Thus the direction (the wave vector k) and the beam direction of rotation in a dextrorotatory substance forms a left-hand system, and in a laevorotatory substance forms a right-hand system. 

M.p. 207°C. The naturally occurring substance is dextrorotatory. Arginine is one of the essential amino-acids and one of the most widely distributed products of protein hydrolysis. It is obtained in particularly high concentration from proteins belonging to the prolamine and histone classes. It plays an important role in the production of urea as an excretory product. 

C(,Hi3N02, CH3 CH2-CHMe-CHNH2-COOH. Colourless crystals, m.p. 284 C (decomp.). The naturally occurring substance is dextrorotatory. An amino-acid, occurring with leucine as a product of protein hydroly-... 

Polarimetric determination of the sucrose concentration of a solution is vaUd when sucrose is the only optically active constituent of the sample. In practice, sugar solutions are almost never pure, but contain other optically active substances, most notably the products of sucrose inversion, fmctose and glucose, and sometimes also the microbial polysaccharide dextran, which is dextrorotatory. Corrections can be made for the presence of impurities, such as invert, moisture, and ash. The advantage of polarization is that it is rapid, easy, and very reproducible, having a precision of 0.001°. 

Comparison of these results indicates identity of the two substances isolated independently by Orekhov and Ehrenstein, but Spiith and Kesztler have suggested that Pictet s nicoteine and Ehrenstein s base, consisted of impure Z-anatabine (p. 46). In this connection it may be noted that Ehrenstein s base was laevorotatory in acid solution, whereas Salts of anabasine are dextrorotatory. These authors have themselves isolated Z-anabasine from tobacco. The identity of synthetic 2-(3 -Pyridyl)piperidine with dZ-anabasine seems to have been definitely established. Anabasis aphylla is the source of the anabasine raanufac-... 

Dextrorotatory (Section 9.3) A word used to describe an optically active substance that rotates the plane of polarization of plane-polarized light in a right-handed (clockwise) direction. 

A substance that rotates plane-polarized light in the clockwise direction is said to be dextrorotatory, and one that rotates plane-polarized light in a counterclockwise direction is said to be levorotatory (Latin dexter, right and laevus, left). 

Halving the concentration or the tube length would halve the number of optically active molecules and the new rotation would be +30° if the substance was dextrorotatory or -150° if levorotatory. 

In the presence of anhydrous hydrogen fluoride at 30°, cellulose is transformed into a polymeric product, called cellan.77 This substance is water-soluble, strongly dextrorotatory ([mineral acid, and only faintly reducing. Molecular-weight determinations (by cryoscopy) on cellan acetate ([a]n + 128°) and on the regenerated polymer indicated it to have a Pn of 14. 

A clockwise rotation, as the observer looks towards the beam, defines the substance as dextrorotatory (i.e., rotates to the right) and the angle a is taken as a positive (+) rotation. If the rotation is counterclockwise the substance is described as levorotatory (i.e., rotates to the left) and the angle a is taken as a negative (—) rotation. 

The beanlike seeds of the trees and shrubs of the genus Erythrina, a member of the legume family, contain substances that possess curare-like activity. The plants are widely distributed in the tropical and subtropical areas of the American continent, Asia, Africa, and Australia, but apparently they are not used by the natives in the preparation of arrow poisons. Of 105 known species, the seeds from more than 50 have been tested, and all were found to contain alkaloids with curariform properties. Erythroidine, from E. americana, was the first crystalline alkaloid of the group to be isolated. It consists of at least two isomeric alkaloids, a and P-erythroidine both are dextrorotatory. Most experimental and clinical study has centered on the b form because it is more readily obtainable in pure state. P-Erythroidine is a tertiary nitrogenous base. Several hydrogenated derivatives of p-erythroidine have been prepared of these, dihydro-P-erythroidine has been studied most carefully and subjected to clinical trial. Conversion of P-erythroidine into the quaternary metho salt (p-erythroidine methiodide) does not enhance, but rather almost entirely, abolishes its curariform activity this constitutes a notable exception to the rule that conversion of many alkaloids into quaternary metho salts results in the appearance of curare-like action. 

The use of this model requires a detailed conformational analysis of flexible molecules to determine whether a given twisted chain of atoms shows a net preference for right- or left-helicity under the influence of chiral centers. Thus, R-2,2,3-trimethyl pentane (3) should exist predominantly in the conformation shown, with the twisted chain of four carbon atoms forming a right-handed helix. The substance is, in fact, dextrorotatory. 13>... 

Optically active substances are termed dextrorotatory (d-) when they rotate plane-polarized light to the right, while laevorotatory (l-) substances rotate it to the left. A mixture of d- and /-forms is called racemic. 

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