Journal
JOURNAL OF CHROMATOGRAPHY A
Volume 1217, Issue 7, Pages 1017-1023Publisher
ELSEVIER
DOI: 10.1016/j.chroma.2009.12.001
Keywords
Axial chirality; Atropisomer; 1,1 '-Binaphthyl; CSP; Stochastic theory; Theoretical plates; BINAP; Racemization; Circular dichroism; Calculated CD spectra
Funding
- Higher Education Commission of Pakistan
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Fast semipreparative HPLC enantioseparation of four axially chiral biscarbostyrils (4,4'-bisquinoline-2-ones) using ULMO as a pi-acidic Pirkle type chiral stationary phase leads to two racernizing pairs (1,2; k(obs) 1.6 x 10(-4) and 3.0 x 10(-4) s(-1) at 28 degrees C) and two stable ones (3,4).3 was stabilized by a crown ether linkage from pos. 6 to 6', and 4 had sterically demanding bromo substituents in pos. 3 and 3'. On-column generated temperature-dependent chromatograms of 1 and 2 were fitted with Auto-DHPLCy2k and DCXplorer. For cpd 2 both programs delivered similar Delta G values of 90 and 93 kJ/mol, well comparable with the 99 kJ/mol calculated with the B3LYP/6-31G (d) procedure. At temperatures of high conversion DCXplorer delivered inconsistent series of rate constants for the more tailing and less resolved tetramethoxy derivative 1. We connect this problem with an almost impossible halfwidth calculation of tailing peak pairs which are weakly resolved. However, this problem could be observed only in the case of tetramethoxy derivative 1. Stochastic generated data of Auto-DHPLCy2k could be used at a lower percentage of conversion only while the theoretical plate model did not deliver useful data at temperatures of very low conversion but fitted well high conversion chromatogram series of 1 and 2. (c) 2009 Elsevier B.V. All rights reserved.
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