Specific rotation alpha

The amount by which a given optical isomer rotates the plane-polarized light is a characteristic signature of that compound or substance. When measured under a set of standard conditions this quantity is termed the specific rotation, alpha, and written in square brackets [ ]. It can be used as a measure of the purity or authenticity of an essential oil in analysis and quality control procedures. This is discussed further in Chapter 5. 

When the original methyl D-fructofuranoside sirup was fermented with yeast, the unstable beta isomer was selectively eliminated and the residue yielded a crystalline methyl D-fructoside melting at 81° and with [a] D +93° in water. The ring structure of this new isomer was proved to be furan by methylation to the liquid tetramethyl derivative, of [a] °D +129.4°, and subsequent hydrolysis to 1,3,4,6-tetramethyl-D-fructofuranose (structure IX) with the correct specific rotation of +29.8° in water. Both the methyl D-fructoside and its fully methylated derivative were therefore of the alpha configuration, since the latter was more dextrorotatory than the tetramethyl-D-fructose and also since the former was more dextrorotatory than the isomer, of [a] D —51°, unstable to invertase. Similar work with the benzyl D-fructofuranoside sirup produced the crystalline alpha isomer, melting point 89°, [a] D +45.7° in water, the liquid tetramethyl derivative, [a] D +83.3° in chloroform and, after acid hydrolysis of the latter, 1,3,4,6-tetramethyl-D-fructofuranose. 

Optical (Specific) Rotation [a] 5 High-Alpha Type Not less than +24°. Low-Alpha Type Not less than +20°. 

First item in a series (for example, the first carbon linked to a carboxyl group). 2. Abbreviation for alpha particle. 3. Symbol for angle of optical rotation. 4. Symbol for degree of dissociation. 5. Symbol for electric polarizability of a molecule. 6. Often with a subscript number (i) the coefficient of [A] in the numerator of the generalized rate expression. 7. Symbol for is proportional to. 8. Symbol for Napierian absorption coefficient. 9. In brackets, symbol for specific optical rotation. 

A display of every atom in a protein is often forbidding and incomprehensible. Viewers are interested in some particular aspect of the structure, such as the active site or the path of the backbone chain, and may want to delete irrelevant parts of the model from the display. Display commands allow viewers to turn atoms on and off. Atoms not on display continue to be affected by rotation and translation, so they are in their proper places when redisplayed. Viewers might eliminate specific atoms by pointing to them and clicking a mouse, or they might eliminate whole blocks of sequence by entering residue numbers. They may display only alpha carbons to show the folding of the protein backbone (refer to Plate 5), or only the backbone and certain side chains to pinpoint specific types of interactions. 

There may be a contrast between the effects of various types of ionization. With a heavy particle such as an alpha particle or a proton the specific ionization is very high, that is, many ions are formed per unit path length. Thus ion-ion, ion-radical, and radical-radical reactions may be very important because concentrations of these intermediates are high. With particles of lower mass, such as photoelectrons, the specific ionization is much lower and the chance of second order effects much less. Thus the effect of specific ionization bears some resemblance to that obtained with rotating sectors and pulse radiolysis. 

When you open your eyes, you will be able to determine that the molecule has been rotated. Specifically, the OH is now on the left side. That is, the two protons on the alpha carbon of ethanol are not interchangeable by rotational symmetry. These protons are therefore not homotopic. Nevertheless, they can be interchanged by reflectional symmetry. Imagine that the molecule is reflected about the plane of the page while your eyes are closed. 

After 300 transfers in the two-phase system iso-octane aqueous buffer pH 8.0 a new component of the hop alpha acids mixture named adhumulone was isolated in 1952 (43). It has exactly the same molecular formula as humulone and the specific optical rotation at the NaQ-line in methanol amounts to -187. The yellow oil can be obtained as a crystalline derivative upon reaction with 1,2-phenylenediamine (melting point 98°C). The spectrometric characteristics and the chemical properties are analogous to those of humulone (44). The only changes in the NMR spectrum relate to the protons in the acyl side chain. The new absorptions are a triplet (3H)... 

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