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A Circular Dichroism Study of Molecular Association of Cinchona Alkaloids and Carboxylic Acids

J. Gawronski ; Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland
M. Brzostowska ; Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland
J. Koput ; Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland

Sažetak

Circular dichroism (CD) spectra of cinchona alkaloids and their salts with carboxylic acids have been investigated. A eontributionof the exciton type Cotton effect to the 230 nm CD band of free bases in non-polar solvents is suggested to result from the association of alkaloid molecules. Strong association is observed in the case of dihydrocupreidine - an alkaloid with free phenolic group.
Comparison of the CD spectra of salts of alkaloids with
mono- and dicarboxylic acids demonstrates that in the latter case
the p-band Cotton effects originate from the exciton type interactions
between the associated molecules.
The unusual rotations of salts of cinchona alkaloids with
biphenyl 1,1'-dicarboxylic acids have been found to originate
from the strong intermolecular exciton coupling, rather than from
the »first-order asymmetric transformation«. The existence of the
two low energy staggered conformations around the C(8)-C(9)
bond in the alkaloid molecule has been confirmed by the MMP2
calculation on a model compound.

Ključne riječi

Hrčak ID:

175384

URI

https://hrcak.srce.hr/175384

Datum izdavanja:

30.6.1989.

Posjeta: 1.129 *