Structure of crown

Fig. 24. Calculated (B3LYP/6-311+G ) structure of crown ether Be2+ complexes (178,182).

X-Ray crystallography has provided a large amount of data on the structures of crown ethers, cryptands and their complexes in the crystal (B-78M152102). The uncomplexed... 

Fig. 11. Structures of crown ethers and cryptands used for isotopic separation...

The overall structure of exo-endo was not unexpected since it is intermediate between the structure of crown (exo-exo) Sg and endo-endo S4N4 (isolectronic with Sg ) as shown in Fig. 9 ... 

Fig. 6 Solid-state structures of crown ethers and several potassium complexes. View this art in color at www.dekker.com.)...

Figure 1. The structures of crown ethers used in this study.

The structures of crown ethers used in this study are shown in Figure 1, In table 1 are shown the results of the qualitative test by the paper disc method. Some alkylbenzocrown ethers (type II and III) and dicyclo-hexylcrown ethers (type IV) showed certain activity. On the other hand, unsubstituted crown ethers (type I) and benzocrown ethers with a polar substituent were inactive. Kryptofix 221 (VI) and Kryptofix 222B, which are highly selective to sodium and potassium, respectively, proved to be inactive, whereas Kryptofix 22DD, which has long alkyl chains, showed some activity. 

Figure 7 Structures of crown ethers coated on ODS colnmn packing. (Reproduced from Ref. 51. American Chemical Society, 1986.)...

Figure 3 Structures of crown ether and derivatives in sensors.

ABSTRACT. The structure of crown ether styryl dyes representing a novel class of dyes is considered. Data on absorption and fluorescence spectra as well as photoisomerization and complexation of photochromic 15-crown-5-ethers are analyzed. The results are exhibited concerning dimerization of the complexes incorporating trans- and cis-isomers of the compounds obtained and stereospecificity of photoinduced cyclodimerization of the latter with formation of cyclobutane derivatives. 

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