Hindered rotation model

The hindered rotation model also assumes bond lengths and bond angles are constant and torsion angles are independent of each other. As its name 

The hindered rotation model assumes independent but hindered roia-tions of torsion angles at constant bond lengths and bond angles with different potential profiles C/(i, ) corresponding to different polymers. The hindered rotation model predicts the mean-square end-to-end distance 

This is the most successful ideal chain model used to calculate the details of conformations of different polymers. In this model, bond lengths I and bond angles d are fixed (constant). 

For a relatively high barrier between trans and gauche states /lE kT the values of the torsion angles ipi are close to the minima (t, g ) [see 

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Derive the characteristic ratio of the hindered rotation model [Eq. (2.40)]. 2.10 What are the common features of all models for ideal linear chains ... 

Scheme la, X = CH3). Well-resolved spectra of propagating radicals of tert-butyl methacrylate (rBMA) have been detected in such polymerization systems at various temperatures as shown in Figure 1,16-line spectra were clearly observed. The spectroscopic feature of the spectra showed a clear temperature dependence which can be interpreted by a hindered rotation model of two stable conformations. The intensity of the inner 8 lines increased with increasing temperature, indicating that there are two exchangeable conformations whose existence have been shown by elucidation of ESR spectra of methacrylates. 

The fact that both heats of formation and equilibrium pressures of the hydrates of spherical molecules correctly follow from one model must mean that the L-J-D theory gives a good account of the entropy associated with the motions of these solutes in the cavities of a clathrate. That the heat of formation of ethane hydrate is predicted correctly, whereas the theoretical value of its vapor pressure is too low, is a further indication that the latter discrepancy must be ascribed to hindered rotation of the ethane molecules in their cavities. 

Hence, the problem is reduced to whether g(co) has its maximum on the wings or not. Any model able to demonstrate that such a maximum exists for some reason can explain the Poley absorption as well. An example was given recently [77] in the frame of a modified impact theory, which considers instantaneous collisions as a non-Poissonian random process [76]. Under definite conditions discussed at the end of Chapter 1 the negative loop in Kj(t) behaviour at long times is obtained, which is reflected by a maximum in its spectrum. Insofar as this maximum appears in g(co), it is exhibited in IR and FIR spectra as well. Other reasons for their appearance are not excluded. Complex formation, changing hindered rotation of diatomic species to libration, is one of the most reasonable. 

Ralph, J. Landucci, L. L. Nicholson, B. K. Wilkins, A. L. Adducts of anthrahydro-quinone and anthranol with lignin model quinone methides. 4. Proton NMR hindered rotation studies. Correlation between solution conformations and X-ray crystal structure. J. Org. Chem. 1984, 49, 3337-3340. 

Peterlin168 has shown that the viscometric data for potato amylose acetate in chloroform solution can be readily interpreted in terms of a random-coil model for the molecule, in which there is hindered rotation at the oxygen atom of the glucosidic linkage. 

Spohr found a significant reduction in the dipole reorientation time for a different model of water (but using the same water/Pt potential). In that paper, the reorientation dynamics are characterized by the spectral densities for rotation around the three principal axes of the water molecule. These calculations demonstrated the hindered rotation of water molecules in the plane parallel to the surface. In addition, a reduction in the frequency of rotation about the molecular dipole for water molecules in the adsorbed... 

The HNMR spectra of the diaqua and aqua (hydroxo) hemin complexes encapsulated in micelles have been reported [20] (Fig. 5). The heme methyl resonances in the diaqua species lie in the same region as those of the high-spin bis(dimethyl sulphoxide) iron (III) porphyrin complex [37-39], while those of the aqua (hydroxo) complex appear in a more upheld region. The positions and linewidths of the heme methyl resonances in these complexes are similar to those observed in the aqua and hydroxo hemoproteins [19,40]. The broadness of the ring methyl resonances of both the diaqua and aqua (hydroxo) species in micelles has been ascribed to arise from the hindered rotational tumbling motion of the heme inside the micelles. The spread and linewidth of these resonances are much larger than those of similar high-spin model heme complexes in simple solution [3]. 

For vapors, the local field vanishes because of the spherical symmetry and eqs A.5 and A.6 provide good agreement with experiment. However, for liquids one can no longer use eq A.6 for the polarizability in the Lorentz— Debye model. Indeed, for liquid water, eq A.5 diverges for values of y about 4 times smaller than the value of y for its vapor, which at 300 K is y = ye 4 yd = 32.3 x 10 40 C2 m2 J "1. One can regard eq A.5 as the definition of the molecular polarizability and calculate y in terms of the macroscopic dielectric constant e. The lower value of the polarizability in liquid than in vapor can be explained in the framework of the Lorentz—Debye model by the hindered rotation of the permanent dipole moment by the neighboring molecules in the condensed state. 

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