Optical rotation observed

Interactive to learn the relationship between observed optical rotation and concentration for optically active compounds. 

One of the terms for describing enantiomer composition is optical purity. It refers to the ratio of observed specific rotation to the maximum or absolute specific rotation of a pure enantiomer sample. For any compound for which the optical rotation of its pure enantiomer is known, the ee value may be determined directly from the observed optical rotation. 

Trialkyl- or triarylallenyltin compounds can also be prepared by Sn2 displacement of propargylic mesylates with various stannylcopper reagents in THF (Eq. 9.82) [71]. This reaction is postulated to proceed by an anti Sn2 pathway based on the stereochemical relationship between the enantioenriched mesylate and the allenic product (Eq. 9.83). The allene obtained from the reaction of the mesylate of (R)-3-phenyl-l-propyn-3-ol with Ph3SnCu was assigned the (P) configuration from a consideration of the observed optical rotation and an application of Brewster s rules [71]. 

In a variation of this method, Tencer and Stein (1978), mixed the isotopic quasi-racemate to near, but not exactly, zero rotation so that at a certain time, tz, the observed optical rotation of the reaction mixture was zero. The equations for this type of kinetic experiment enable one to calculate the difference between the individual isotopic rate constants from tz and the ratio of rate constants (the KIE) from te and tz provided that the ratio of the initial rotations for the two isotopic substrates is known. Usually it is preferable to... 

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 ... 

When the specific rotation ([a]) of a pure liquid is reported (indicated by the term neat) its density dmust be referred to. An error is introduced into the specific rotation when the density measurement is inaccurate. Therefore, the rotation of a pure, undiluted sample can be quoted in an alternative way by the observed optical rotation a and the cell path length l (in decimeters). A typical standard form for correctly reporting the specific rotation of a pure liquid is as follows for trans- —)-(2S. 3S)-2.3-dimethyloxirane34 (ee >99%) ... 

The effects of wavelength of the light in the polarized beam on the magnitude and sign of the observed optical rotation are considered in Section 19-9. 

Observed optical rotation during glucosidase-transferase hydrolysis of phosphorylase limit dextrin (15)... 

Restricted rotation, as surface conjestion increases, was postulated as being responsible for the observed optical rotations as the generations increase,1251 the possibility of racemization during amino acid acylation was also investigated. Amino acid isolation and high-performance liquid chromatography (HPLC) analysis following acidic hydrolysis of the asymmetric dendrimers revealed an enantiomeric excess > 96 %. 

In units of degrees, the observed optical rotation (a) is given by ... 

We observed optical rotation in the recovered carbonyl compound when an enamine, as the salt of an optically active acid, was hydrolyzed. An example of this is illustrated in Figure 1 (J), where the racemic carbonyl compound must be chiral. 

In a stereoselective reaction, one stereoisomer is formed in a major amount than another. When the stereoisomers are enantiomers the selectivity is known as enantioselectivity. The degree of enantiomeric purity of a solution is measured by its enantiomeric excess, or ee. The percentage enantiomeric excess is found by dividing the observed optical rotation by the optical rotation of pure enantiomer in excess and multiplying by 100. 

Only the methoxy- and chloro-compounds (38, 3 ) exhibit large deviations between calculated and observed rotations. In general, the 1,1-diphenylcyclopropanes XVIII have rather large optical rotations ( [ ]d > 90°). Inspection of Table 3 reveals that the molar rotations of XVIII are almost entirely due to helix optical activity ( 0 q > 0 d ). This is in contrast to an earlier assumption which has attributed optical rotations of XVIII to atomic asymmetry. Further comparisons between calculated and observed optical rotations of complex cyclopropanes I are presented in Table 4. 

Since the magnitude of the Effect is proportional to the concentrations of both the environment substance and the complex, a series of equations have been developed for observed Pfeiffer rotation, specific Pfeiffer rotation, and molar Pfeiffer rotation which are analagous to those for observed optical rotation, specific optical rotation, and molar optical rotation (3.it,6,10). These are... 

THE PFEIFFER EFFECT WITH (+)D-TARTARIC ACID OBSERVED OPTICAL ROTATION IN DEGREES... 

Obtained in aq soln only. Shows no observable optical rotation. Is condensed with phosphoenolpyruvate by a cell-free extract from an E. coli mutant to give a 90% yield. 

Because the stereochemistry is fixed at all three chiral centers of the molecule, one would expect to observe optical rotation by the molecule. The optical rotation of pergolide mesylate was measured with the sodium d line (589 nm) as the light source at a concentration of 10 mg/ml in dimethylformamide (DMF) in a 100 mm cell using a Perkin-Elmer Polarimeter Model 241MC. The specific rotation measured at 20°C has been observed to be between -18.0 and -23.0°. 

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