Silicas amide functional types

In order to broaden the capabilities of the Pirkle concept, both polar and polarizable groups were introduced into the molecule. The most popular of this type of chiral stationary phase are the (R,R) Whelk-01 and the (S,S)Whelk-01 phases, the structures of which are shown below. These phases are more versatile and have a wider field of application than the phases previously described. The phases are covalently bonded to the silica and so they can be used with almost any type of solvent. However, they have been found to operate most effectively in the normal phase mode. It should be noted that the polarizable character of the aromatic ring is essential for the stationary phase to function well. As the Pirkle phases are generally available in both the (R) and (S) configurations, the reversal of the elution order of a pair of enantiomers is possible. This stationary phase was originally designed for the separation of the Naproxen enantiomers but has found a wide application to the separation of epoxides, alcohols, diols, amides, imides and carbamates. 

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