Abstract
A series of compounds were studied which had increasing alkyl chain length between an aromatic group and a tertiary amine. In this homologous series, a maximum in retention versus alkyl chain length was found for a wide range of mobile phases using either a silica gel column or a cyanopropyl-bonded silica gel column. One nonaqueous mobile phase using an octadecyl-bonded silica gel column also showed this maximum. The selectivity between E and Z geometric isomers found with the shorter chain analogues decreased with increasing chain length greater than about pentyl, with eventual complete loss of resolution. A few normal-phase solvents produced a reversal of the usual E−Z elution order. 1H NMR assignments are described for the individual geometric isomers. NMR studies and ab initio calculations indicate that a folded conformation in solution is possible for the longer chain analogues. The unusual retention patterns are most likely due to a combination of localized adsorption and analyte solution conformation effects.
Published Version
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