Orientational isomers

Nishioka and Fujita 78> have determined the Kd values for a- and P-cyclodextrin complexes with m- and p-substituted phenols at pH 7.0. Taking into account the directionality in inclusion of a guest molecule, they assumed three and two probable orientational isomers for the cyclodextrin complexes with m- and p-substituted phenols respectively (Fig. 6). Then the observed Kd values were divided into two or three terms corresponding to the dissociation of the orientational isomers involved (Eqs. 16, 17) ... 

Fig. 6. Probable orientational isomers for cyclodextrin complexes with m- and p-substituted phenols...

Fig. 12. A portion of the 500 MHz DEFT-NOESY spectrum of NPl-ImH, recorded at 30°C in 50 mM phosphate buffer, pH 7.0, D2O. Note the strong EXSY cross peak between the 3-Me signal at 24.9 ppm and a minor 3-Me signal at 26.4 ppm. This is not the other heme orientational isomer, as is evident by comparison of spectrum (a) of Fig. 11. This chemical exchange is also observed for many protein side chains, suggesting fluxionality of some loop, probably the A-B loop that passes close to the heme. In the text, the small peak is defined as species Y, and the large as species X. ...

Are products with different sugar conformations and/or base orientations (isomers) formed ... 

Pairs of frequencies attributed to ethyl orientational isomers. 

Figure 5 Synthesis of two oriental isomers of a [2]rotaxane reported by Isnin and Kaifer.

The viscosity dependence of emission from the charge-transfer complexes of tetracyanoethylene with benzene and a number of alkylbenzenes has been studied. At high viscosities the fluorescence spectra of alkylbenzenes have a double-band character and the two sub-bands change in different ways with changing viscosity. These observations and the dependence of the excitation spectrum on observation wavelength are discussed in terms of different orientational isomers of the ground-state charge-transfer complexes.1 7... 

Oxy-y-butyrolactones are substructural units in many biologically interesting natural products, accessible by nucleophilic addition of the enolates of tert-butyl acetate on epoxy pentuloses. The hthium enolate of ferf-butyl acetate is reacted with the epoxy ketose 50 (generated from 49) in a mixture of THF/HMPA (3 1) to afford 51 and 52. However, the frans-oriented isomer 52 can only be converted to the desired lactone 54 on treatment with TFA in CH2CI2 at room temperature for 30 min [18] (Scheme 11). 

H. Higuchi, T. Ishikura, K. Miyabayashi, M. Miyake and K. Yamamoto, Synthesis and properties of orientational isomers of hybridized dihexylbithiophene-octaethylporphyrin connected with 1,3-butadiyne linkages. Tetrahedron Lett, 40, 9091-9095 (1999). 

Scheme 29.2 Formation of the two possible pseudorotaxane orientational isomers derived from the calix[6]arene wheel 4 and the non-symmelric axle 5 2TsO carrying only one stopper...

Fig. 29.4 (Top) Representation of the two pseudorotaxane orientational isomers, up and down , that can form tluougli the threading of the non-symmetric wheel 4 with monostoppered rivet-like non-symmetric axles 5-2TsO, 9-10 2TsO and ll 2TsO TFA...

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