Solvent rotation temperature

Iwata K, Ozawa R, Hamaguchi H (2002) Analysis of the solvent- and temperature-dependent Raman spectral changes of S1 trans-stilbene and the mechanism of the trans to cis isomerization dynamic polarization model of vibrational dephasing and the C=C double-bond rotation. J Phys Chem A 106 3614—3620... 

The observed optical rotation is dependent on both the wavelength of the light and the temperature. The sodium D line (589 nm) is usually used to make measurements. The solvent in which the sample is dissolved may also greatly affect the [a] of a substance. Values for [a] are usually quoted with details of the concentration of the solution used for measurement, the solvent, the temperature and the type of light used. For example the specific rotation for (-) adrenaline is given as ... 

The specific rotation [a]f is an inherent physical property of an enantiomer which, however, varies with the solvent used, temperature T in °C), and wavelength of light used (A), It is defined as the observed rotation per unit length of light path, per unit concentration (for a solution) or density (for a pure liquid) of the enantiomer thus ... 

P up to 90 (by vapor-phase osmometry). The structures of the polymers, as indicated by their optical rotation, were strongly influenced by changes in the reaction conditions (especially by the temperature and polarity of the solvent). Lower temperatures (—78°) gave rise to higher yields and greater Pn- No epimerization occurred during polymerization, other than that at the anomeric carbon atom. 

The deposition of thin solid polymer films by the SCO process is illustrated in Figure 1. A fixed volume of a viscous solution of the polymer to be deposited is placed on a flat substrate, such as a silicon wafer, and then rapidly rotated. Depending on the solvent volatility from the solution and such parameters as initial volume of solution, initial concentration of solids, the substrate temperature relative to the boiling point of the solvent, rotational speed, and spinning duration, a wet or dry polymer film results. 

Because amines are subject to hydrogen bonding, the shift depends on concentration, solvent, and temperature. Amide, pyrrole, and indole NH groups absorb from — 6 8.5 to 5.0 the effect on the absorption position of concentration, solvent, and temperature is generally smaller than jin the case of amines. The nonequivalence of the protons on the nitrogen atom of a primary amide and of the methyl groups of A Af-dimethylamides is caused by slow rotation around the C—N bond because... 

The three basic conformational isomers of chloramphenicol are shown in Figure 2. In solution, the rotamers (a), (b), and (c) are expected to be in equihbrium and the concentration of any one of the three species at any given time is dependent on the nature of the solvent and temperature. Chloramphenicol has a specific rotation, [a], of -Hl8.5° in ethanol and —30° in dimethyl formamide (22). 

This method appears simple, yet several precautions are necessary. Apart from the fact of knowing the specific rotation of the pure enantiomer, which is itself not always straightforward, the measurement of the optical rotation must be made under the same conditions of solvent, concentration, temperature and wavelength as were used to obtain the specific rotation of the pure enantiomer. Moreover, the measured rotation is often weak, which increases the error in the measurement. It also happens not infrequently that the complexes being studied are strongly coloured, and as a result the measurement is not possible with a standard polarimeter. The presence of impurities with a large optical rotation may also invalidate the reading. 

I- Laevorotatory optical rotation at a specified wavelength, solvent and temperature,... 

Determination of barrier to internal rotation.-Temperature dependence for ion pairs with K and Mg in etheral solvents also shown. 

Apart from NMR and die mefliods suitable for characterization of overall chain dimensions (which we will touch on below), fliere are not many simple experimental techniques that can be used to study sugar conformation and that are directly correlated to theoretical results based on calculated potential energy surfaces or force fields. An exception is given by chiro-optical techniques, which provide important (although empirical) structural information as optical rotation experiments have been shown to be very useful and informative in flic study of saccharides in solution. Literature gives die experimental evidence for the effects of the external conditions (solvent and temperature) on the optical rotation. The additivity mediods, proposed in the Fifties by Whiffen and Brewster, " were... 

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