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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 19, Number 1
BKCSDE 19(1)
January 20, 1998 

An NMR Study on Complexation of Ethylammonium Ion by Alkyl p-tert-Butylcalix [6]aryl Ester Derivatives
Sangdoo Ahn, Chul Soon Mun, Kee Choo Chung, Weon Seok Oh, Suk-Kyu Chang, Jo Woong Lee*
The complexation of ethylammonium ion by alkyl p-tert-butylcalix[6]aryl ester derivatives was studied via measurements of proton and carbon spin-lattice relaxation times (T1) and chemical shift changes in solution state (CDCl3). The results indicate that the endo-type omplexes are formed and that the overall tumbling rates of these complexes are more rapid than those of the corresponding free hosts. The association constants for these complexes in THF-d8 were determined by 1H NMR titration at several different temperatures to estimate the relevant thermodynamic parameters. The logK's for ethylammonium complexes of methyl, ethyl, and propyl esters at 313 K, for example, were found to be 1.56, 3.41, and 3.08, respectively. The complexes formed may be thought of as being kinetically stable in view of their 1H NMR behavior in 2 : 1 host/guest solution.
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