Conformation contribution

This expression accounts for the configurational entropy of an ideal binary mixture with identical molecular sizes, but not for that of a polymer solution, since polymer chains are large and flexible. For that case, more contributions arise from the chain conformational entropy, first considered by Meyer [19] and then derived by Huggins [20] and Flory [21]. In analogy with a nonreversing random walk on a lattice, the conformational contribution of polymer chains to the partition function is given by... 

An important property of chain molecules is that a major contribution to the standard entropy is conformational in nature, i.e. is due to hindered internal rotations around single bonds. This property is most relevant to cyclisation phenomena, since a significant change of conformational entropy is expected to take place upon cyclisation. Pitzer (1940) has estimated that the entropy contribution on one C—C internal rotor amounts to 4.43 e.u, A slightly different estimate, namely, 4.52 e.u. has been reported by Person and Pimentel (1953). Thus, it appears that nearly one-half of the constant CH2 increment of 9.3 e.u. arises from the conformational contribution of the additional C—C internal rotor. 

Failure of a critical chloride transport protein to fold properly into its functional conformation contributes to many cases of cystic fibrosis (CF), which is the most common fatal inherited disorder of white people. 

In the case of flexible molecules all chiral conformers contribute to the observed CD spectrum. This usually leads to substantial reduction of the magnitude of the exciton Cotton effect. Nevertheless, if the conformation of the main contributor is established independently (e.g.. by molecular mechanics or NMR spectroscopy), its absolute configuration can be deduced from the exciton Cotton effect. Thus, for 3-(l-naphthalenyl)phthalide 5, the preferred conformation is 5 a. The negative couplet is in accordance with the left-handed screw between the phthalide 1 Ld and the naphthalene lBb transition dipole moment vectors, when the absolute configuration is R121. 

Aberle, T., Burchard, W., Vorwerg, W., Radosta, S. (1994). Conformational contributions of amylose and amylopectin to the structural properties of starches from various sources. Starch/Stdrke, 46, 329-335. 

Conformational contribution to the entropy and energy of fusion of isotactic PP. 

Sci 43, 1-32 (1942)] by taking account of leading chain-conformational contributions to Si(x). 

The two diastereoisomers of the dihydropyran-3-one (203) also exhibit different conformational preferences in solution (82JOC3054). Although the conformer with the aryl group pseudoaxially oriented is predominant for the cis isomer, both conformers contribute significantly to the conformational equilibrium associated with the trans isomer. 

Another problem that has not yet been solved is the flexibility of the oligosaccharide bonds. Due to their population, the different conformers contribute to the physical observables and a change in the predicted properties is expected, but only when the minimum energy conformation is taken into account or when the total conformer distribution is used. 

D. Horton and J. D. Wander, Calculation of molecular rotation by summation of partial conformational contributions. Part 2. Rotation of the l,6-anhydro-deoxy-/i-D-hexopyranoses, 2,7-anhydro-/i-D-heptulopyranoses, and their acetates, Carbohydr. Res., 14 (1970) 83-94. 

However, a number of tris-chelate mixed ligand Cr(III) complexes do exhibit a correlation of the same signs between the lowest frequency 2E component and the major 4E component.119,120,122,123 This relation has been verified by examining the CD for diastereomers of [Cr(en)x(diamine)3 x]3 + (x = 0, 1, 2), c/i-[Cr(NH3)2 (diamine)2]3 +, where the diamines used were (R)- or (5)-propylenediamine and (IR,2R)- or (15,250-1,2-traras-cyclohexanediamine. The differences in CD patterns between each pair of the diastereomers were accounted for by separability and additivity of the configurational and conformational CD contributions. The CD in the spin-allowed 4T2 <— 4A2 transitions shows a positive major component (4E) for the configurational contribution and a minor negative (4Ai) and major positive (4E) components from the lower frequency side for the conformational contribution as shown in Figure 5.30. 

Stancik, A. L., and Brauns, E. B. (2008). Rearrangement of partially ordered stacked conformations contributes to the rugged energy landscape of a small ma hairpin. Biochemistry 47, 10834—10840. 

C, the dipolar interaction is not responsible for the large peak width for the amorphous phase in this case. The chemical shift is affected by the conformation of the polymer. In the amorphous phase, the polymer chain takes several con-formers or makes rapid transitions between a number of conformational states. In this case, the distribution of the conformation contributes to the peak width of the amorphous phase. 

In the epoxidation of the corresponding highly crowded Z-isomer144 the force field (vide supra) predicts a greater number of conformers contributing to the overall difference of activation enthalpy for the formation of the diastereomers the calculated ratio of 93.5 6.5 in favor of the (20/ )-isomer is compatible with the reported isolated yield. This enhancement of stereodifferentiation by cis substitution contrasts with the behavior of uncrowded alkenes (vide supra). 

In the related tricyclic framework of the two epimeric silphiperfolcncs 7 agreement with reported isolated yields169 is almost perfect in both epimers three conformers contribute to the favored and four conformers to the disfavored mode of attack. 

An extremely large number of conformations contributes to the profile (z). Two of them are the completely flat conformation (with till segments in layer t) and the completely perpendicular one, with only the first (or last) segment... 

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