Rotation observed

The direction and the degree to which a compound rotates plane-polarized light is given by its observed rotation. 

When a photon reflects off any molecule, the orientation of the electric field produced by that photon is rotated. The mirror image of that molecule will rotate the electric field to the same degree but in the opposite direction. In a typical compound where a photon is just as likely to collide with either mirror image, there are so many millions of molecules producing so many collisions that the photon is most likely to leave the compound with the same electric field orientation with which it 

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The observed rotation a of an optically pure substance depends on how many mol ecules the light beam encounters A filled polarimeter tube twice the length of another produces twice the observed rotation as does a solution twice as concentrated To account for the effects of path length and concentration chemists have defined the term specific rotation, given the symbol [a] Specific rotation is calculated from the observed rotation according to the expression... 

Cholesterol when isolated from natural sources is obtained as a single enantiomer The observed rotation a of a 0 3 g sample of cholesterol in 15 ml of chloroform solution contained in a 10 cm polarimeter tube is -0 78° Cal culate the specific rotation of cholesterol... 

The specific optical rotations of pure a and p o mannopyranose are +29 3° and -17 0° respectively When either form is dissolved in water mutarotation occurs and the observed rotation of the solution changes until a final rotation of +14 2° is observed Assuming that only a and p pyranose forms are present calculate the percent of each isomer at equilibrium... 

Polarimetry. Polarimetry, or polarization, is defined as the measure of the optical rotation of the plane of polarized light as it passes through a solution. Specific rotation [ a] is expressed as [cr] = OcjIc where (X is the direct or observed rotation, /is the length in dm of the tube containing the solution, and c is the concentration in g/mL. Specific rotation depends on temperature and wavelength of measurement, and is a characteristic of each sugar it may be used for identification (7). 

The solvolysis of 2, 35-3-(4-methoxyphenyl)but-2-yl/>-toluensulfonate in acetic acid can be followed by several kinetic measurements (a) rate of decrease of observed rotation (k ) rate of release of the leaving group (k,) and, when 0-labeled sulfonate is used, the rate of equilibration of the sulfonate oxygens (k ). At 25°C, the rate constants are... 

A specimen obtained by tbe reduction of limonene tetrabromide by Godlewski and Eoshanowitsch had a specific rotation + 125° 36 which is practically equal to an observed rotation of + 106° 30, thus confirming the purity of the specimens prepared by fractional distillation. 

The amount of rotation observed in a polarimetry experiment depends on the number of optically active molecules encountered by the light beam. This number, in turn, depends on sample concentration and sample pathlength. If the concentration of sample is doubled, the observed rotation doubles. If the concentration is kept constant but the length of the sample tube is doubled, the observed rotation is doubled. It also happens that the amount of rotation depends on the wavelength of the light used. 

To express optical rotations in a meaningful way so that comparisons can be made, we have to choose standard conditions. The specific rotation, [a ]D, of a compound is defined as the observed rotation when light of 589.6 nanometer (nm 1 nm = 10-9 m) wavelength is used with a sample pathlength / of 1 decimeter (dm 1 dm = 10 cm) and a sample concentration C of 1 g/mL. (Light of 589.6 nm, the so-called sodium d line, is the yellow light emitted from common sodium lamps.)... 

A 1.20 g sample of cocaine, fa-]D = -16, was dissolved in 7.50 mLof chloroform and placed in a sample tube having a path length of 5.00 cm. What was the observed rotation ... 

The upper state can also be formed in energetically excited ro-vibrational states. Most photoelectron experiments do not have enough resolution to observe rotational levels, except in rare cases, but vibrational resolution is commonly achieved. Therefore, it is possible to carry out limited vibrational spectroscopy of cations and reactive neutral molecules using this approach. 

In this relationship, a is the observed rotation, d is the path length, s is the concentration of the solution in g solute/mL solution, a is the concentration in g solute/g of solution, and p is the density of the solution. The most commonly used light source is the sodium lamp, which has X = 589 nm. Therefore, designations of a specific rotation are indicated by the use of symbols such as ( + )589-[Co(en)3]3 +. ... 

Optical activity Experimentally observed rotation of the plane of monochromatic plane-polarized light to the observer s right or left. Optical activity can be observed with a polarimeter. 

In 1965, Denney et al. (98) reported the reaction of a number of alkenes with ferf-butyl hydroperoxide (TBHP) and cupric salts of chiral acids. The use of ethyl camphorate copper complex 144 in the allylic oxidation of cyclopentene provides, upon reduction of the camphorate ester, the allylic alcohol in low yield and low selectivity, Eq. 82. The initial publication only provided the observed rotation of cyclopentenol, but comparison to subsequent literature values (99) reveals that this reaction proceeds in 12% ee and 43% yield (based on the metal complex). 

The maximum observed rotation for the 2-amino-2-methyl-1-propanol salt of levopimaric acid is [a] n —218°. Methanol and ethanol solutions give the same specific rotations, but methanol is the preferred solvent because the time required to effect solution in ethanol is longer. If pure levopimaric acid, m.p. 151-153°, [a] D —276° is desired, the salt with —210° rotation should be dissolved in 8 parts of boiling methanol, the solution concentrated to the point of incipient crystallization, cooled, and filtered. The yield in this recrystallization is about 70%. 

Recent microwave data for the potential interstellar molecule Sis is used together with high-level coupled-cluster calculations to extract an accurate equilibrium structure. Observed rotational constants for several isotopomers have been corrected for effects of vibration-rotation interaction subsequent least-squares refinements of structural parameters provide the equilibrium structure. This combined experimental-theoretical approach yields the following parameters for this C2v molecule re(SiSi) = 2.173 0.002A and 0e(SiSiSi) = 78.1 O.2 ... 

The purpose of this report is to demonstrate the ease with which highly accurate equilibrium structures can be determined by combining laboratory microwave data with the results of ab initio calculations. In this procedure, the effects of vibration-rotation interaction are calculated and removed from the observed rotational constants, Aq, Bq and Cq. The resulting values correspond to approximate rigid-rotor constants and and are thus inversely... 

Optical activity is the ability of a compound to rotate the plane of polarized light. This property arises from an interaction of the electromagnetic radiation of polarized light with the unsymmetric electric fields generated by the electrons in a chiral molecule. The rotation observed will clearly depend on the number of molecules exerting their effect, i.e. it depends upon the concentration. Observed rotations are thus converted into specific rotations that are a characteristic of the compound according to the formula below. 

The observed rotation in degrees is divided by the sample concentration (g ml ) and the sample tube length (decimetres). The unusual units used transform the measured small rotations into more manageable numbers. The specific rotation is then usually in the range 0-1000° the degree imits are strictly incorrect, but are used for convenience. The polarized light must be monocbromatic, and for convenience and consistency the D line (589 nm) in the sodium spectmm is routinely employed. Both the temperature and solvent may inflnence the rotation somewhat, so mnst be stated. 

Bickait (258) relates to magnitudes of optical activity well below the detection limits of the available instmments. It plays a role in the examination of polymer chirality and will be discussed later. Our attention will be focused on those polymers that display observable rotation and are, therefore, necessarily chiral. A clear separation among these classes of polymers—stochastically achiral, cryp-tochiral, and chiral—can be made with reference to a suitable model. 

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