Circular Dichroism Studies of Crown Complexed Ion Pairs: A Comparison of the Alkali and Alkaline Earth Nitrate Complexes of Chiral Crown Ethers

: A series of four chiral 18-crown-6 macrocycles, (2S,6S)-2,6-dimethyl-l,4,7,10,13,16-hexaoxacyclooctadecane and its (2R,3R)-2,3-dimethyl isomer and (2S,6S‘,11S’,15S)-2,6,11,15-tetramethyl-l,4,7,10,13,16-hexaoxacyclooctadecane and its (2R,3R, 11R,12R)-2,3,l 1,12-tetramethyl isomer, have been synthesized. Complexes of these crowns with alkali and alkaline earth nitrate ion pairs have been characterized in chloroform solution, with particular emphasis on the induced circular dichroism (CD) observed in the nitrate n→π* transition. The nitrate CD spectra observed for the alkali complexes are distinctly different from those of the corresponding alkaline earth complexes. The sign and intensity patterns in the CD have been interpreted in terms of the coupled oscillator theory for host-guest complexes. Structures based on the CD data for these ion pairs in solution have been proposed and compared to crystal structure data. © 1986, American Chemical Society. All rights reserved.

Duke Scholars

Author Richard A. Palmer Chemistry