Benzoates, conformational analysis

The special electronic structure of the anomeric center in pyranoid derivatives results in experimentally significant differences in molecular geometry (e.g., as reflected by bond lengths and valence angles) about the anomeric carbon atom between a- and 0-pyranoses and a- and /3-pyranosides. In the article by Jeffrey, a discussion of the structural properties of the anomeric center in pyranoses and pyranosides is given, and a comparison is made of crystallographic data of some carbohydrates with the results of theoretical calculations performed on model compounds. Paulsen and co-workers also present x-ray crystallographic data in their discussion of some aspects of the conformational analysis of pentopyranosyl acetates, benzoates, and halides, in comparison with extensive conformational data compiled by Durette and Horton for these compounds in solution. 

Aspects of Conformational Analysis of Pentopyranosyl Acetates, Benzoates, and Halides... 

Conformational analysis of pentopyranosyl acetates, benzoates, and halides has been reviewed. ... 

X-ray analysis of 4,4-dimethylandrostan-3-on-17/3-yl benzoate (67) that the A ring is in a deformed chair conformation (225) in the crystal, and NMR and dipole moment measurements show the same to be true in solution. 

The most frequently used acyl derivatives, i.e., benzoates and cinnamates substituted in the 4-position, are listed in Table 7. The analysis of the stereochemistry of the bichromophoric system including a benzoate (cinnamate) chromophore is greatly simplified by its preference for s-trans conformation at the C(0)-0 bond, in which the carbonyl group is staggered ca. 30° to either side of the carbinyl C H bond. Consequently the direction of the electric dipole moment of the charge-transfer transition is approximately parallel to the C(H)-Q bond (Figure 16). 

A vast array of covalent molecules have been synthesised over the years in the search for LCs that show the useful cholesteric and ferroelectric smectic C phases, often on a trial and error basis ignoring the interactions between the molecules. The idea that one could think of the interactions between the molecules as a kind of molecular recognition came from the careful analysis of the conformations of molecules in the layers [77,78]. The arguments are based on the symmetry limitations of the angle formed by the alkyl chain and the phenyl benzoate moiety in the molecules that were the subject of this study. A molecular recognition site within the phase was used as the basis for these speculations , which have actually proved rather successful. The actual interactions between molecules are usually weak, but the formation of layers of aromatic and aliphatic units in these mesophases gives rise to their unique properties. 

By means of X-ray structure-analysis, we were able to determine the conformation and arrangement in the crystalline state both of the benzoates and the acetates. It was demonstrated that the tribenzoates favor the tetraaxial conformation, whereas the triacetates crystallize favorably in the tetra-equatorial form, even though the tetraaxial form predominates in solution (JO. 

Crystals of 43, suitable for X-ray diffraction analysis, were grown by slow diffusion of pentane into a solution of 43 in THF. The structure was elucidated by single crystal X-ray diffraction, which reveals that compound 43 adopts a wing-like conformation (Figure 30). Crystals of the tetrabutylammonium benzoate complex of 43 were... 

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