Conformation of compound

The conformational statistics of asymmetric vinyl chains such as P2VN are well-known 126). The rotational conformers of isotactic (meso) dyads are entirely different from those of syndiotactic (dl) dyads. Frank and Harrah132) have described each of the six distinct conformers for meso and dl dyads, using the t, g+ and g nomenclature of Flory 126). Excimer-forming sites (EFS) are found in the tt and g g+ meso states, and in the degenerate tg , g t dl state. Because the rotational conformers of compounds such as l,3-bis(2-naphthyl)propane do not match those of either the iso-or syndiotactic dyads of P2VN, the propane compounds make poor models of aryl vinyl polymers. However, the rate constants of fluorescence and decay of the intramolecular excimer in polymers can usually be determined from the propane compounds (but see the exceptional case of PVK and its models133)). 

FIGURE 6. Structure and equilibrium conformation of compounds 15-27. Reproduced by permission of Elsevier Science from Reference 43... 

DISCO considers three-dimensional conformations of compounds not as coordinates but as sets of interpoint distances, an approach similar to a distance geometry conformational search. Points are calculated between the coordinates of heavy atoms labeled with interaction functions such as HBD, HBA or hydrophobes. One atom can carry more than one label. The atom types are considered as far as they determine which interaction type the respective atom would be engaged in. The points of the hypothetical locations of the interaction counterparts in the receptor macromolecule also participate in the distance matrix. These are calculated from the idealized projections of the lone pairs of participating heavy atoms or H-bond forming hydrogens. The hydrophobic points are handled in a way that the hydrophobic matches are limited to, e.g., only one atom in a hydrophobic chain and there is a differentiation between aliphatic and aromatic hydrophobes. A minimum constraint on pharmacophore point of a certain type can be set, e.g. if a certain feature is known to be required for activity [53, 54]. 

Deprotonation takes place in all the complexes shown above the anions participate as ligands and not as neutral initial molecules 14-16. Other examples of change of composition and structure, in particular tautomeric forms and conformations of compounds used as ligands, are also known [11,16,21,22]. This principal difference between compounds used as ligands and ligands themselves should always be taken into account. Nevertheless in some cases, due to plain convenience, we have kept unchanged the traditional use of the concept of ligands. ... 

Thus, the main factors determining the conformation of compounds with isolated or cumulated sulfur-sulfur bonds are the bond distance d,... 

Although structural conformation of compounds of this invention were confirmed by 500 MHz H-NMR in d -DMSO, spectra were not supplied by author. Derivatives, however, were used in skin lotion formulations and results provided. 

The physical methods used for the analysis of carhohydrate conformations are becoming increasingly sophisticated as the molecules studied and the questions asked become larger and more complicated. X-ray crystallography provides a reference point, the conformations of compounds in the solid state. In solution, molecular modeling supplies a framework which can be used to interpret the results of the vast array of NMR spectral observations and those from other methods. For reviews, see [2,354]. 

Similarly, the CC conformation was found for compounds 52 and 53 in the solid state (X-ray data) (50). Compound 52 was found by variable temperature H-NMR spectroscopy to undergo a rapid base-induced intramolecular 3,7-hydride shift (the associated activation energy is AG1 = 19.4 0.2kcal mol1 at 113°C)(51). The CC conformation of compounds 54 (52) and 55-58 (4) and the CB conformation of compound 59 (4) found in solution by analysis of 13C-NMR spectra are as expected. However, the preference for the CC conformation was discussed on the basis of 13C-NMR data for the... 

The preferred conformation of compounds 200 and 201 (from X-ray data) is determined by the configurations of the 2- and 4-phenyl groups the exo,exo arrangement of these groups destabilizes a CC conformation and leads to a CB conformation (200) (144). 

The solution conformations of compounds analogous to 200 and 201 and of the corresponding 9-hydroxy analogs, and the role of hydrogen bonding in the... 

Sulfoxide 218 exists both in solution (from H-NMR data) and in the solid state (from X-ray data) in a chair-chair conformation (162,163) that is, the change in valence state of one sulfur atom stabilizes the CC conformation. The chair-chair conformation was unexpectedly found for compound 219 despite the strong interaction of lone-pair orbitals of the sulfur atoms demonstrated by photoelectron spectroscopy (164,165). The S3- -S7 distance is equal to 3.37 A. Thus, the presence of sulfur atoms solely at the 3- and 7-positions is insufficient to destabilize a CC conformation heteroatoms must be present at other positions. The chair-boat conformation of compound 220 (from X-ray data) was explained by steric and dipole-dipole interactions (166). 

The important role of a heteroatom at the 1-position is demonstrated by the CB conformation of compound 242 in the solid state (188). The presence of a N-l, C-2 amide bond makes it somewhat similar to bridgehead olefins of type 101. 

Relative Energies (in kcal mol ) of the CC, BC, CB, and TT Conformations of Compounds 243-248 Calculated Using the Molecular Mechanics (MM1) Method (22)... 

Of the four conformationally locked analogues related to compound 59, only the isomer 64 with the benzamide and aryl piperazine functionalities both in an equatorial conformation had comparable binding and functional activity. This was consistent with the notion that 59 was bound to the DA D2 receptor in an extended conformation. Energy-minimized structures of 59 and 63-66 were modeled to determine the distance between the aryl centroid of the benzamide and the basic piperazine nitrogen atom (Figure 6). For 64 the distance was 11.8 A and corresponds to the distance observed in the extended conformation of compound 59,... 

Fig.(6). Conformation of compounds 24 and 25 deduced from NOESY spectra.

R)-Spirobi-1,4-dioxan (212) has been prepared from 2-chloro-ethyl 3-D-fructopyranoside.220 A study of the half-chair conformations of compounds (213 X and Y = or S or S02 R1, R2=a variety of substituents or benzo) has been made using H n.m.r. spectros-copy,221 and the conformation of dibenzo-1,4-dioxin is folded about the 0-0 axis at an angle of 16S3 according to an n.m.r. study.222 Tetrachlorodibenzodioxin is a very stable compound but electrolysis in the presence of other oxidizable compounds breaks down the molecule.22 3... 

Since the stablest conformation of compounds of this type (as well as anions) is determined by a stabilizing interaction between a nonbonding HOMO level and a superjacent (LUMO) level, David et al. (175), to describe such interaction, proposed the term superjacent orbital control. 

MNDO calculations have been performed on various conformations of compounds of type (29), and these values have been compared with experimental data derived from variable-temperature NMR <94JPR177>. Selected conformations of caprylolactam (10), as found by a molecular mechanics search, were examined using MNDO-AMl <90MI 927-01 >. 

TABLE 4. Calculated barriers to libration" (kcalmol" ) in gauche and anti conformations of compounds RCMc2—CMc2R... 

Qualitative and quantitative assessments of equilibrium mixtures of Amadori rearrangement products were performed employing C-NMR spectrometry [64]. Substituents at C-6, C-4 and C-6 showed considerable influence on the equilibrium the 4,6-0-benzylidene derivative, for example, was found to be in the open-chain form only, because ring closure of 0-5 with the carbonyl function was energetically and sterically hindered. The conformation of compounds substituted at C-6 depended on the electron-withdrawing effect of the substituent. The lower the electron density at position C-5, the lower is the tendency of ring closure, so that the equilibrium is found on the side of the open-chain form. 

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