Conformational similarity analysis

Obtain the energy for axial methylcyclohexanone, and use equation (1) to calculate the room temperature equilibrium distribution of equatorial and axial conformers. Is the amount of the axial conformer significant (>5%) Perform a similar analysis as above and decide which face of the carbonyl in the axial conformer is more likely to undergo nucleophilic attack. Does addition lead to the same alcohol as before ... 

A similar analysis has been carried out for pentacoordinate nitrosyls (37) and precise rules were derived for the preferred conformations, on orbital interaction grounds alone. 

Recently, a similar analysis of the conformational energy has been performed also for various new syndiotactic polymers.27,47 The conformational energy maps of syndiotactic polypropylene (sPP),48 polystyrene (sPS),49 poly butene (sPB),25 and poly(4-methyl-l-pentene) (sP4MP)26 are reported in Figure 2.12. A line repetition group s(M/N)2 for the polymer chain, and, hence, a succession of the torsion angles. .. 0i, 0i, 02, 02,..., has been... 

A similar analysis in terms of conformational dynamics can be performed as well for the interpretation of neutron scattering data in the picosecond time window159 and dielectric data.156 How do these findings then... 

A similar analysis can be performed for the cases where X is an unsaturated group, 1. e. C CH, H2C=CH, C=N. The microwave spectrum for the cases where X is a cyano140,141 or alkynyl group142 shows that the most stable conformation is the eclipsed one as predicted by OEMO theory ... 

By a similar analysis of the results for the traus-1,2-difluoropropene, (3), and the antiperiplanar conformation of 1,2-difluoropropane, (7), (see also Table 5) one can see that the previous findings are still valid when the LDBS scheme is apTJ/pT/[pD/m]/m. However, it can he seen in Figs 3 and 7 that for quantitative reproduction of the vicinal F-F coupling it is necessary to describe the carbon atom of the CH3 substituent with a larger than a minimal basis set. In both cases, the cc-pVDZ basis set was used. 

A second strategy to control facial selectivity involves the use of chiral sultams and lactams as auxiliaries for the dipolarophile (120-123). Cycloaddition of 132 with a variety of substituted nitronates provides up to 9 1 selectivity of the major diastereomer (Table 2.38). However, substitution at the a-position of the dipolarophile leads to a reduction in stereoselectivity (entry 5). Assuming an s-cis conformation of the dipolarophile, it is proposed that the major isomer arises from an endo approach of the nitronate to the Re face of the dipolarophile (Fig. 2.13). This is supported by X-ray crystallographic analysis of one of the cycloadducts, which resides in a conformation similar to the proposed transition state. However, this analysis assumes that the silyl nitronate is only reacting through the... 

A similar analysis predicted that isomer 26 should exist in the conformation 26A (0 kcal/mol) whereas isomer 27 should exist as conformer 27A (4.8 kcal/mol). However, since isomers 26 and 27 are interconvertible under acid-... 

A similar analysis of data obtained from molecules with asymmetric end groups is more complicated. Apart from the problems connected with the separability of the torsional motion from the framework vibration, experience shows that several more terms have to be included in the Fourier series to describe the torsional potentials properly. On the other hand, the electron-diffraction data from asymmetric molecules usually contain more information about the potential function than data from the higher symmetric cases. In conformity with the results obtained for symmetric ethanes the asymmetric substituted ethanes, as a rule, exist as mixtures of two or more conformers in the gas phase. Some physical data for asymmetric molecules are given in Table 4. The electron-diffraction conformational analysis gives rather accurate information about the positions of the minima in the potential curve. Moreover, the relative abundance of the coexisting conformers may also be derived. If the ratio between the concentrations of two conformers is equal to K, one may write... 

Similar analysis of spectral data was used to secure the structure of the novel alkaloids androbiphenyline (13) and colchibiphenyline (14), which exist in CDCI3 solution as an almost equal mixture of atropoisomers. Esterification and O-methylation of 13 and 14 afforded derivatives which were almost exclusively present in conformation b, with the acetyl protons appearing at 8 1.58 ppm (Fig. 2). 

The conformation of C-lactose (25a, R = H) bound to peanut lectin agglutinin has been studied through X-ray analysis.11 The bound conformation, defined by o —63, I c 120°, is practically identical to that of the parent O-lactose (25b, R = H) bound to the same protein. ( o —69, I c 118°). The authors were tempted to conclude from this particular observation that the conformational similarity in protein-bound states is a general phenomenon. Nevertheless, it is clear that the architecture of the binding site should also be analyzed (see later). In contrast, Espinosa et al.12 and Asensio et al.90 demonstrated that the three staggered conformations of C-lactose (syn-exo-<(>, syn- it syn-exo-d>, anti- H and anti-exo-, syn-ty) are recognized by three different proteins, and in some cases their behavior differs from that with natural lactose. 

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