12-Crown-4, conformational analysis

Grant, G. J., Shoup, S. S., Baucom, C. L., and Setter, W. N. (2001) Complexation and conformational analysis studies of 11-membered ring crown trithioethers, Inorg. Chim. Acta 317, 91-102. 

Vyacheslav V. Samoshin was born in Norilsk, Russian Federation. He graduated with an Honorable Diploma (M.S.) from Moscow State University in 1974. At the same university, he defended his Ph.D. dissertation under the supervision of academician Nikolay S. Zefirov in 1982, and his Doctor of Chemical Sciences dissertation in 1991. He worked as a researcher in the Department of Chemistry, Moscow State University, and since 1992 as professor (head of the Division of Organic Chemistry in Moscow State Academy of Fine Chemical Technology). In 1999, he took his present position as professor of chemistry at the University of the Pacific, Stockton, California. His scientific interests include molecular switches, conformational analysis, synthesis and studies of bioactive compounds, including carbohydrate mimetics, asymmetric synthesis, and synthesis and studies of crown ethers and relative compounds. 

Conformational analysis of free and complexed crown ethers in solution 91JPR817. 

Bis(crown ethers) connected by a flexible spacer are a source of intramolecular sandwich-type complexes with alkali metal ions <1992MI1>. A conformational analysis (based on a combination of semiempirical and ab initio methods) performed on 12-crown-3 38 and 12-crown-4 39 predicted that, in the case of sandwich-type complexation, the nucleophilic cavity of 12-crown-3 rather than that of 12-crown-4 is more prone to complexation with the Na+ ion. Accordingly, ion-selective electrodes based on bis(12-crown-3) derivatives with dialkylmalonate spacers displayed the highest selectivity for Na+ ions among the alkali and alkaline earths investigated, and superior to the Na+ selectivity reached with the bis( 12-crown-4) analogue <2003ANA(480)291>. 

As the receptors have become more complex, forces such as H-bonding and dipole-dipole interactions have augmented the ion-dipole complexation mechanism typical of crown ethers. This has increased the importance of conformational analysis for the receptors and an understanding of structure. Ultimately, however, the binding of a guest by a host molecule is defined by the equilibrium constant for that system in a particular solvent and at a specified temperature. 

Considerable effort has been made with regard to conformation analysis of crown thioethers. It has been found that ligand strain is most evident in torsion angles, whereby an examination of the deviations from the optimum values of... 

The earliest studies on the IR spectra of crown ethers and their complexes were carried out by Pederson (B-78MI52101). Since then IR spectroscopy has been applied a number of times to solve structural problems in crown ether chemistry including ion pair interactions and conformational analysis (B-79MI52103). A low frequency vibration of the cation within the macrocycle has been identified which is dependent on the cation but not on the solvent (214 cm for Na -dibenzo[18]crown-6 in both DMSO and pyridine). This is in contrast to the frequency of cation vibration within a solvent cage, which for Na is 202 cm in... 

Weiner et al. (32) have described the application of distance geometry to the conformational analysis of cyclooctane, cyclododecane, 18-crown-6, and... 

The (Z)-stilbene (6) does not form a rotaxane with dibenzo-24-crown-8 but, when the stilbene is isomerized (sensitized by benzil) to the E form, a pseudo-rotaxane is formed.Lewis and Crompton have reported that the photoacidity of the stilbene derivatives (7) and (8) is dependent on the position of the hydroxy group on the stilbene, and as a consequence the meta derivative undergoes isomerism.The influence of the nitrogen atoms on the photochemistry of the 1,4-distyrylbenzene analogue (9) and related compounds has been assessed. The photophysics and conformational analysis of the stilbene dimer (10) have been studied. Modelling of the optical properties of the stilbenophane (11) has been reported. 

A different conformational picture is encountered when the eight-membered ring is fused with two aromatic rings as illustrated by the conformational analysis on the dibenzo[d ][l,3>6]dioxazocine (7) skeleton carried out by Farkas et al. <85JST131>. The possible structures can be divided into the quasi-rigid Q symmetric butterfly conformation (7a), which has the hetero ring in the crown conformation, and two flexible conformational families with an enantiomeric relationship... 

A number of theoretical and experimental approaches toward conformational analysis of crown thioethers have been developed. A molecular mechanics force field for thiols and thioethers, developed from crystal structures and experimental data <87JST(I59)I37> reproduces molecular structures and provides reasonable fits for both the energy differences between conformers and barriers to internal rotation. Thioethers with gauche placement at carbon-sulfur bonds were calculated to be 0.69 kJ mol more stable than those with anti placement, in agreement with earlier SCF-MO calculations <85MP33l). 

The cyclodecanone ring of ( )-3P-hydroxy-5,10-seco-l(10)-cholesten-5-one was shown to adopt an extended crown conformation by an A -ray structure determination of its p-bromobenzoate. In contrast, analysis of the and n.m.r. spectra of its acetate showed two conformations to be present in solution, the major one (85%) corresponding to the extended crown observed in the solid state, and the minor one corresponding to conformation (23). The failure of force-field calculations to reproduce the energy differences between different conformations was attributed to a transannular interaction between the double bond and the carbonyl group. The observed conformations were used to rationalize the stereochemistry of several reactions of these seco-steroids. ... 

Holzberger A, Holdt HJ, Kleinpeter E (2004) Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II)-an experimental solution NMR and theoretical molecular modelling study. Org Biomol Chem 2(12) 1691-1697. doi 10. 1039/B402224F... 

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