Enrichment factor rotations

Siddall and his co-workers (46) have examined the barriers to rotation of a series of 2,6-disubstituted anilides. Af-Ethyl-A/-(2,6-xylyl)formamide (9) was recrystallized as a uranyl nitrate complex, and one isomer, which at equilibrium was favored by a factor of 3 1, was enriched up to a 30 1 ratio. The kinetics of rotation were examined at 0 to 29°C. The Arrhenius activation energy was 26 3 kcal/mol and log A was 18.5 2.4 hr-1. Siddall and Gamer (47) were able to obtain an almost pure isomer (which also predominated at equilibrium 1.3 1 for the ethyl compound and 1.1 1 for the methyl compound) of Ar-alkyl- V-(2-methyl-4,6-dibromophenyl)-l-naphthamide (10). The half-lives of... 

Irradiation performed with racemic substrate at room temperature, unless noted otherwise. Anisotropy (g) factor at or around irradiation wavelength, if reported or estimated. Extent of destruction. Maximum observed rotation a of irradiated solution, or specific rotation [a] of isolated sample or of residue obtained upon evaporation. Maximum observed ellipticity of irradiated solution or molar ellipticity of isolated sample. Enantiomeric excess of isolated sample. Not reported. Compound (mp 113 C) of unknown structure, obtained in a reaction of humulene with sodium nitrite, according to the reported procedure Chapman, AC. J. Chem. Soc. 1895 67 780. A mixed case of asymmetric destruction and photoderacemization irradiation performed at 0 C. Enantiomerically enriched sample used. Estimated g factor enhanced by two-quantum excitation with high intensity picosecond laser pulse. High-inten-sity laser of indicated pulse duration used. "Irradiation performed at 77 K in a hydrocarbon glass matrix. Optically pure sample photolyzed only to evaluate the enhanced g factor. Estimated g factor enhanced by two—quantum excitation with high-intensity femtosecond laser pulse. 

The template 7a can be split off by water or methanol to an extent of up to 95% (Scheme 2-5). The accuracy of the steric arrangement of the binding sites in the cavity can be tested by the ability of the polymer to resolve the racemate of the template, namely of phenyl-a-D,L-mannopyranoside. Therefore the polymer is equilibrated in a batch procedure with a solution of the racemate under conditions under which rebinding in equilibrium is possible. The enrichment of the antipodes on the polymer and in solution is determined by measuring the specific optical rotation and the separation factor a, i.e., the ratio of the distribution coefficients of the D and L compounds between polymer and solution, is calculated. After extensive optimization of the procedure, a values between 3.5 and 6.0 were obtained [10]. This is an extremely high selectivity for racemic resolution that cannot be reached by most other methods. 

The fundamental chemical principle behind the isotopic offset between the two aqueous boron species relates primarily to vibrational and rotational energy differences between the two isotopes, such that the heavier isotope is preferentially incorporated into the trigonal species. The motivation for studying this fractionation was for the nuclear industry, as has a very high cross section for neutron captme, and so is used as a neutron flux absorber. Mechanisms for enriching from natural boron led to studies that showed it could be separated from "B on ion exchange columns. Theoretical approaches were used to calculate the fractionation factor a, which describes the isotopic offset between two phases. 

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