Intramolecular conformational change

These expressions demonstrate that the change of entropy and internal energy on deformation under these conditions is both intra- and intermolecular in origin. Intramolecular (conformational) changes, which are independent of deformation, are characterized by the temperature coefficient of the unperturbed dimensions of chains d In intermolecular changes are characterized by the thermal expansivity a and are strongly dependent on deformation. The difference between the thermodynamic values under P, T = const, and V, T = const, is vefy important at small deformations since at X - 1 2aT/(/,2 + X — 2) tends to infinity. 

The last line in Table I presents decay parameters for a dimer in which all 10 hydroxyl groups have been acetylated. Acetylation reduces Ti and T2, but there is not much change in and a 2. More importantly, acetylation increases the size of the energy barrier that must be surmounted when the dimer undergoes the conformational transition from one rotational isomer to the other. For this reason, the rate of intramolecular conformational change is much slower in the peracetylated dimer than in the free phenol forms it is slow enough so that 400-MHz proton NMR can resolve distinct signals from the two rotational isomers in dioxane-ds solution 10). The... 

A similar two-step mechanism of gelation through coil-helix transition was confirmed for synthetic polymers with stereo-regularity. For instance, in solutions of syndiotactic poly(methyl methacrylate) (PMMA) in toluene, a fast intramolecular conformational change is followed by the intermolecular association leading eventually to gelation [49,50]. 

Single stranded strnctme. For an intramolecular conformational change such as a single stranded sequence folded back on itself ... 

Bending is an intrahelical conformation change characterized by a curvature in the phosphate backbones. Condensation is an intramolecular conformation change involving the collaptse of a molecule into a sphere or a toroid. 

CIO7, or Cl", deposited in a conducting film generated by copolymerization of the ruthenium complex with e.g., pyrrole or 3-methylthiophen, when this film is immersed in acetonitrile. Displacement of chloride is slower when the appropriate film is immersed in water this aquation process is photo-catalyzed." Variable-temperature NMR has given some information on intramolecular conformational changes in the constrained ligands (62) and (63) [X=—CHj— to — (CH2)4—]. The inversion barrier of 44kJmol" ... 

Similar experiments have been carried out with poly(3,3 -azodibenzoyl-fra 5 -2,5-dimethylpiperazine) and poly(4,4 -azodibenzoyl-rrfl/i5-2,5-pipera-zine) see Structures (4) and (5) [6,9]. In each one there was a reduction in viscosity with irradiation. However, the change was very small (less than 10% at 0.538 g/dL ) compared with that of the aforementioned system. Moreover, no difference was detected between the intrinsic viscosities measured in the dark and under irradiation. These results suggest that the pho-toinduced decrease in the viscosity of Structures (4) and (5) arises from an interchain interaction and not from an intramolecular conformational change. 

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