Abstract
Summary The chiral selectivities of two optically active selectors, binaphthyl-2,2′-diyl hydrogen phosphate (binaphthylphosporic acid, BPA) and 2-(2,4,5,7-tetranitro-9-fluorenylideneaminooxy)propionic acid (TAPA), are compared. Whereas all carbo- and heterohelicene selectands can be resolved on TAPA columns, only helicenes containing heteroatoms or electron-donating substituents could be easily separated on BPA. Resolution factors ( r ) for several sulphur-, bromine- and nitrogen-containing helicenes on coated and linked BPA and TAPA columns are given. The highest resolution factor was obtained for 9,10-diaza(7,8;11,12)dibenzo-heptahelicene ( r = 1.60) on a TAPA column silanized with N-2-(aminoethyl)aminopropyl and methyl groups (1:4) before coupling with the selector. Lowering the column temperature to 2° allowed the partial resolution of some carbohelicenes on BPA. Steric and binding requirements for chiral recognition between selectors and selectands and the influence of environmental changes (spacer length, mobile phase, mode of selector application) on the resolution process are discussed.
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