Single-conformer model

Three conformers A with nearly C2 symmetiy, B with Cj symmetry ( = 131.4(30)°, 62 = 80.4(52)°) and C with Ci symmetiy (0i = 101.1(98)°, 82= 196.8(24)°) fitted the experimental data almost equally well any mixtures of them cannot be excluded on the basis of ED data. The conformer A from the single-conformer model was slightly favoured. 

Macrocyclization equilibrium data from metathesis reactions of cycloolefins are compared with predictions of a novel, simple RIS scheme for polyalkenes with at least three single bonds between adjacent double bonds. The predictions agree with experiment within the combined experimental errors, supporting the conformational models and confirming that macrocyclization equilibrium has indeed been established in the metathesis reactions. 

Bond length and bond angles are kept fixed at values used earlier (Suter, U, W. J. Am. Chem, Soc. 1979, 101, 6481). For the CH2-CH2 bonds three approximately staggered conformations are appropriate. At first, rotation about CO-CH2 bond is subdivided Into the same three isomeric states, but In the course at the calculations it becomes clear that the trees region cannot be satisfactorily modeled by a single conformation. The region is consequently split Into three equal domains, so that five rotational isomeric states result g" 0 to - 120°, t" - 120° to - 160°, t0 - 160° to 160°, t+ 160° to 120°, g+ 120° to 0°. 

Fig. 1. Various conformation models for macromolecules adsorbed on an interface, a) chain lying totally on the interface b) loop-train conformation c) loop-train-tail conformation d) adsorbed at one chain end e) random coil adsorbed at a single point f) rod-like macromolecules adsorbed at one end g) rod-like macromolecules adsorbed located totally on an interface...

The unfolded state U is modeled as a single conformation even though this is by no means obvious and usually cannot be verified. The unfolding equilibrium between N and U can be shifted to the unfolded form by measures such as an increase in temperature or an increase in the concentration of structure breakers , termed chaotropes, such as urea or guanidinium hydrochloride. When either temperature or the concentration of chaotropes is decreased (or the concentration of structure formers , kosmotropes, is increased), the folding equilibrium reverts to the native state N. The two-state model is an approximation very often, analytically verified folding intermediates render the two-state model incomplete. 

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