ABSTRACT
We present herein new analytical protocols for the separation and structural elucidation of polyphenyls. Three commercially available chromatographic stationary phases are compared in the separation of these non-polar, unfunctionalized, positional isomers. Baseline separation of nine terphenyl and quaterphenyl isomers is achieved in under ten minutes using a rapid gradient elution HPLC method. Complete separation of these, and a further five polyphenyls, is demonstrated. We finally present a linear correlation between solvent accessible surface area and the retention times of these closely related compounds.
Subject(s)
Chromatography, High Pressure Liquid , Chromatography, High Pressure Liquid/methods , Solvents/chemistryABSTRACT
A bis-oxazoline ligand has been complexed using Cu(ii) and Zn(ii) trifluoromethanesulfonate and a range of chiral ionic liquid (CIL) additives based on natural products were used as a co-catalyst for a Diels-Alder reaction. The catalytic performance of these systems was compared for the asymmetric Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene with and without the presence of a CIL additive. In the absence of the CIL, both catalysts resulted in low enantioselectivities in conventional solvents and ionic liquids. However, whilst only a minor effect of the CIL was observed for the Cu based catalyst, in the case of the Zn based catalyst, significant enhancements in endo enantioselectivity of up to 50% were found on the addition of a CIL.
ABSTRACT
The activation energy for hydrogen abstraction from imidazolium-based ionic liquids is significantly higher than that observed in conventional solvents.
ABSTRACT
A total of 374 patients were followed up for at least 10 years after tubal ligation, and 43% required further gynaecological treatment. Major gynaecological surgery was needed by 25%. There seems a good case for the selective use of hysterectomy as a method of sterilization.