Conformational isomerism, hydrogen bonds

Figure 6.43 Conformational isomerism, hydrogen bond exchange and HH-transfer in N,N -di-(p-F-phenyl)amidine (DFFA) dissolved in tetrahydrofuran (S) according to Ref [24cj.

Diheterolevulosans, 209-211, 240 Dihexulose dianhydrides, 207 -266, see also Caramels Di-D-fructose dianhydrides 13C NMR spectra, 245-246 conformation, electronic control, 224-228 conformational rigidity, energetic outcomes, 228 hexulopyranose rings, 226 historical overview, 210-213 H NMR spectra, 248 -249 intramolecular hydrogen-bonds, 227 isomerization, 231 -232 1,2-linked, ero-anomeric effect, 224-225 listing, 240-241 nomenclature, 208-210 optical rotations and melting points, 242-243 protonic activation... 

Furthermore, it is often possible to extract from the structural analysis of solid solvates a significant information on solvation patterns and their relation to induced structural polymorphism. An interesting illustration has been provided by crystal structure determinations of solvated 2,4-dichloro-5-carboxy-benzsulfonimide (5)35). This compound contains a large number of polar functions and potential donors and acceptors of hydrogen bonds and appears to have only a few conformational degrees of freedom associated with soft modes of torsional isomerism. It co-crystallizes with a variety of solvents in different structural forms. The observed modes of crystallization and molecular conformation of the host compound were found to be primarily dependent on the nature of the solvent environment. Thus, from protic media such as water and wet acetic acid layered structures were formed which resemble intercalation type compounds. 

Amino-acul complexes. frans-(0,X)-[CoX(aminoacidato)(dien)]Y (X == CN, NO2, or Cl Y = Br, Cl, or ClO aminoacid === Gly, a-aminobutyric acid, L-Ala. L-Val, L-Thr, or L-Pro) complexes have been isolated. The cyano-complexes were shown to exist in the new conformational isomeric endo- and cxo-forms. This refers to the position of the hydrogen atom bonded to the central N of dien w ith respect to the cyanide group. The tetramine ligands 1,3-diaminopropane, 3,7-diaza-l,9-nonanediamine (2,3,2-tet), and 4,7-diaza-1.10-decanediamine (2,2,3-tet) exhibit marked topological specificity in the complexes [Co(tetramine)(aa)] (aa = Gly. Ala, Val. or Sar). Thus a-[Co-(3,2,3-tet)aa] and P2-[Co(2,3,2-tet)aa] appear to be formed exclusively under the synthetic conditions employed. 

Of the three stable conformers of HO—ONO, the (cis,cis) conformer with a five-membered hydrogen-bonded ring lies lower in energy than the others. Three different channels in the isomerization process of HO—ONO were found. The (cis,perp) is a bridge transferring from (trans,perp) to the (cis,cis) conformer . 

Conformational isomerism in propane Propane is a three-carbon- (sp -hybridized) atom-containing linear alkane. All are tetrahedrally arranged. When a hydrogen atom of ethane is replaced by a methyl (CH3) group, we have propane. There is rotation about two C-C cr bonds. 

Conformational isomerism in cyclopropane Cyclopropane is the first member of the cycloalkane series, and composed of three carbons and six hydrogen atoms (CsHe). The rotation about C-C bonds is quite restricted in cycloalkanes, especially in smaller rings, e.g. cyclopropane. 

Fig. 8. Replication. The amino adenosine X and the pentafluorophenyl ester Y form a hydrogen-bonded dimer XY, prior to reaction between the amine and the activated ester groups (shown in the circle). The reaction product is a at-amide conformer cis-Z that isomerizes to the more stable trans-amide Z. The replicative process is catalyzed by the reaction product Z (also referred to as the template). First, a termolecular complex XYZ is formed from X, Y, and Z.

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