Bond Lengths and Valency Angles

The accuracy of a crystal-structure analysis depends on (1) the magnitude and distribution of the experimental errors in the measurements of the x-ray diffraction spectra (2) the ratio of the observational data/ variable parameters and (3) the completeness of the computational treatment of the data. 

Since the later 1930s, not much progress has been made toward increasing the accuracy of the measurements of the diffracted intensities, although it 

Bond Lengths and Angles in Pyranoid Sugars and Derivatives 

Pyranoid sugar or sugar residue Derivative studied Bond length (A.) Angles degrees) At carbon At in rings Or References 

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B. Molecular Geometry Bond Lengths and Valence Angles.345... 

C16H2207 l,5-Anhydro-2,3,4-tri-0-benzoylxylitol (ATBXYL10)114 PI Z = 2 Dx = 1.32 R = 0.053 for 3,536 intensities. The crystal structure contains centrosymmetrically related d and l enantiomers. The pyranoid conformation is an almost ideal (d) [1C4(l)]i withQ = 60 pm, 0=1°, with normal bond-lengths and valence-angles. The benzoyl groups are equatorial, with their planes approximately normal to the mean plane of the pyranoid ring. 

Data concerning the X-ray-determined structures of derivatives of 1-telluracyclohexane of the general formula 18 are relatively scarce. Some data on bond lengths and valence angles in 18 are listed in Table I. 

An X-ray crystal structure study of the bromine adduct of 3,5-diphenyl-1,2-oxatellurolyl-l-ium bromide 27 has also been reported (86JOC1692). The bond lengths and valence angles within the five-membered ring in 27... 

Mean values of the bond lengths and valency angles are given. 

Many X-ray structural investigations of type 92 heterocycles have been carried out with the exclusion of phenothiatellurine. Data on bond length and valency angles are given in Table VI. 

The mean values of bond lengths and valency angles are given. Data for the 2,8-dimethyl-/V-ethylphenotellurazine. c Data for the perfluorotellurantrene. 

Bond lengths and valence angles are also given in Tables 1 and 2. 

Table 2 contains data on bond lengths and valence angles of the tellurophene ring. 

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. 

In this paper, we will be concerned with the molecular geometry, as described by the torsion angles, bond lengths and valence angles associated with the anomeric carbon atom in a and 3 pyranosyl compounds, I and II. The Pauling... 

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