Phenyl group rotations

During transformation from the neutral molecules to the corresponding anion-radicals, the rate of the fragment rotation, relative to one another, decreases. This also results in the nonequivalence of the meta and ortho protons. Thus, 3-acetylpyridine gives two different anion-radicals as conformational isomers (Cottrell and Rieger 1967). In the case of 3-benzoylpyridine anion-radical, the phenyl group rotates freely about the carbonyl center, whereas the rotation of the pyridyl group is limited. The ESR spectrum shows that the spin density in the phenyl ortho positions is half of that... 

A similar scale drawing of 1,3,5-triphenylbenzene, Figure 8-3, shows that there is some steric repulsion between hydrogen atoms in this molecule (drawn with nonbonded radius 1.0 A) the same amount is expected for biphenyl (Fig. 8-4). Triphenylbenzene has been shown by an x-ray study to be nonplanar,84 with two of the phenyl groups rotated through about 30° in one direction and the third rotated by 27° in the other direction. The gas molecule has been shown by elec-... 

Michler s ketone MK also shows a dual fluorescence in alcohols, and, in this case, the bridged model compound MKB is available which clearly demonstrates that (1) a blocking of the phenyl group rotations (around the C-C bonds) blocks the channel toward the TICT state, and (2) the... 

Phenyl group rotation can be characterized from the phenyl carbon Tj s by assuming the segmental description developed from the proton data (5). Either segmental model can be used, and the corresponding correlation times for internal rotation of the phenyl group by stochastic diffusion, t j-p s, are displayed in Table II and Table III. Again both approaches match the observed... 

Properties.—Carbon-13 and field-dependent proton spin-lattice relaxation times have been measured as a function of temperature and molecular weight for solutions of polycarbonates in CDCI3. The spin-lattice relaxation times were interpreted in terms of segmental motion, characterized by the sharp cut-off model of Jones and Stockmayer, for phenyl group rotation and methyl group rotation. ... 

The applications of these techniques is illustrated by data on a variety of polymers, although the bulk of the discussion concerns a typical amorphous polymer, atactic polystyrene and a crystalline polymer, polyethylene oxide. A number of results are quoted which seem to indicate that phenyl group rotations or oscillations are not an important mechanism in the relaxation of polystyrene. Other materials mentioned are polypropylene oxide, starch and ionized copoly-... 

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