Backbone configuration, and

Table I shows the molecular weights and the relative photographic speed results of the amorphous p-methoxycinnamate polymer films. The difference in the photographic speed between polymers X and XIA, XIB could be attributed to the difference in the backbone configuration and the effect it has on the orientation of the cinnamate chromophore as well as the M.W. difference.

Seebach, D., Sifferlen, T., Mathieu, P. A., Hane, A. M., Krell, C. M., Bierbaum, D. J., and Abele, S. (2000). CD spectra in methanol of /3-oligopeptides consisting of /3-amino acids with functionalized side chains, with alternating configuration, and with geminal backbone substituents. Fingerprints of new secondary structures Helv. Chim. Acta 83, 2849-2864. 

Hoffmann, H. M. R. Dunkel, R. Mentzel, M. Reuter, H. Stark, C. B. W., The total synthesis of C-glycosides with completely resolved seven-carbon backbone polyol stereochemistry Stereochemical correlations and access to L-configured and other rare carbohydrates. Chem. Eur. J. 2001,7, 4771-4789. 

Lysine 41 is not in contact with the phosphate or sulfate in the p, site. It is nicely constrained by the structure so that it cannot be in contact without a gross fluctuation (backbone motion) from the average structure derived in the X-ray analysis. Cyclization of 3 -CMP would require appreciable rotation around the C2 -C3 bond, around the C3 -03 bond, and around the 03 -P bond. The phosphorus must move approximately 2 A relative to the 02 -C2 -C3 -03 configuration, and if B and R, do not move then the P04 would move directly toward Lys 41 and potentially make contact. 

In a typical analysis of a polymer chain, the experimental values of configuration-dependent properties and their temperature coefficients are compared with the results of rotational isomeric state calculations. These comparisons yield values of the energies for the various rotational states about the backbone bonds, and these conformational preferences can then be used to predict other configuration-dependent properties of the chains. It is also possible to obtain such conformational information from potential energy calculations, using the methods of molecular mechanics.39,46 52... 

Among the factors affecting the course of the RCM reaction, those depending on substituent configuration and/or functional group protection are among the most difficult to anticipate. Several cases illustrate the important influence on the course of the reaction of apparently insignificant structural modifications to the precursor backbone. 

There is a basic difference between rupture above the glass transition temperature (where the polymer backbones have an opportunity to change their configurations before the material fails) and well below Tg (where the backbone configurations are essentially immobilised within the period of observation brittle materials). 

D. Seebach, T. Sifferlen, P. A. Mathieu, A. M. HSne, C. M. Krell, D. J. Bierbaum, S. Abele, CD Spectra in Methanol of P-Oligopeptides Consisting of P-Amino Acids with Functionalized Side Chains, with Alternating Configuration, and with Geminal Backbone Substituents - Fingerprints of New Secondary Structures , Helv. Chim. Acta 2000,83,2849 -2864. 

Geselowitz et al. (200) showed that the oxidation of A,A-[Co(en)3] by A[Co(edta) ]" results in the production of A[Co(en)3] in excess of the other enantiomer, and vice versa for A[Co(edta)] . The enantiomeric excess was around 9% in H2O but rose with decreasing solvent polarity to 40% in sulfolane. The substitution of the en backbone of edta with alkyl groups has a negligible effect on the enantiomeric excess of [Co-(enlal or on the rate of the reaction. This seems to be evidence for the view that the selectivity arises from the pre-equilibrium step of the reaction and that [Co(edta)] and analogues were oriented with a carboxylate face toward the [Co(en)3] ion. The same conclusion was reached (221) in the study of the ion pair formation between [Co(edta) ] and [Co(en)3] + that is, that the stronger ion pairs were formed between complexes of opposite absolute configuration and that [Co-(edta) ] associated via its pseudo-C3 carboxylate face. 

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