Specific rotation definition

An optically active Grignard reagent has the ability to differentiate between the two enantiofaces of a carbonyl compound such as 45 [64], In the example shown, the (S)-enantiomer of the product alcohol, 46, is obtained with a high degree of optical purity (= specific rotation of mixture- - specific rotation of one pure enantiomer X 100 for definitions of other terms used in this work, see [65]). 

Final Caution. The Student t distribution is to be used when the numerical value to which it attaches is a mean of a definite number of direct observations or is a numerical result calculated from such a mean by a procedure that introduces no uncertainties comparable in magnitude to the random errors of the direct observations. This is notihe case for the specific rotation [a]j discussed above. The uncertainty contribution to the final result that is due to random errors in the raw data on optical rotations Oy is not large compared to the contributions due to the estimated uncertainties in the other variables (particularly Vand Z) that are required for calculating the final result The number of degrees of... 

The most definitive stereochemical studies have concerned configurational changes at the a carbon. Alexander et al. (2, 138) showed that (-I-)540-CpFe(CO)2CH(Me)Ph reacts with neat SOg at —60° or — 10°C, or with SO2 in saturated pentane at 27°C, to give the corresponding iS-sulfinate. The specific rotation of the product, [a]546, varied somewhat with the method of synthesis (—186°, —176°, and —158°, respectively). It was concluded that the insertion is a substantially stereospecific process, but whether it involves retention or inversion could not be determined. 

Palytoxin is a white, amorphous, hydroscopic solid that has not yet been crystallized. It is insoluble in nonpolar solvents such as chlorophorm, ether, and acetone sparingly soluble in methanol and ethanol and soluble in pyridine, dimethyl sulfoxide, and water. The partition coefficient for the distribution of palytoxin between 1-butanol and water is 0.21 at 25°C based on comparison of the absorbance at 263 nm for the two layers. In aqueous solutions, palytoxin foams on agitation, like a steroidal saponin, probably because of its amphipathic nature. The toxin shows no definite melting point and is resistant to heat but chars at 300°C. It is an optically active compound, having a specific rotation of -i-26° 2° in water. The optical rotatory dispersion curve of palytoxin exhibits a positive Cotton effect with [a]25o being -i-700° and [a]2,j being +600° (Moore and Scheuer 1971 Tan and Lau 2000). 

The optical purity is usually, but not always, equal to enantiomer excess. In order for the two to be equal, it is necessary that there be no aggregation. It is possible, for example, that a homochiral or heterochiral dimer (see Glossary, Section 1.6, for definitions) would refract the circularly polarized light differently than the monomer (or each other). In 1968 [19] Krow and Hill showed that the specific rotation of (S)-2-ethyl-2-methylsuccinic acid (85% ee) varies markedly with concentration, and even changes from levorotatory to dextrorotatory upon dilution. In 1969 [20], Horeau followed up on Krow and Hill s observation, and showed that the optical purity (at constant concentration) and enantiomer excess of (5)-2-ethyl-2-methylsuccinic acid were unequal except when enantiomerically pure or completely racemic. This deviation from linearity is known as the Horeau effect, and its possible occurence should be remembered when determining enantiomeric purity by polarimetry. 

Having established these stereostructures of degradatiOTi products 116 and 117 was the definitive proof of the stereostructure of a- and p-lipomycin. We felt utterly reUeved that they coincided with the configurational assignments based on the specific rotations of our synthetic and Zeeck s analytical samples. To be honest, we were as close to saying mission accomplished as can be... 

The modern definition of specific rotation [a] of a liquid for a given wavelength (A. in nm) and temperature (t in °C) was also introduced by Biot as follows ... 

A sesquiterpene has been isolated from the essential oil of Cannabis Indica. This may fairly be considered a definite body, as it has been isolated by many different observers and described by them at different times. Valenta first mentions it. Vignolo describes it as a mobile liquid boiling at 256°, of specific gravity -897 at 15°, and slightly laevo-rotatory. Wood, Spivey, and Easterfield give the boiling-point as 258° to 259°, the specific gravity as -898 at 18°, and the rotation as - 8-6°. 

Let us now apply the technique in some specific cases. The existence of optical activity of several compounds in solution has been explained due to the presence of several active forms of the compound in equilibrium with each other and various assumptions about the forms were also put forward. The equilibrium between the different forms depended on external conditions. But a definite explanation was put forward in 1930 about tartaric acid and it was said that the molecule exists in the following three conformations and each of which makes a certain contribution to the rotation observed. 

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