Carbonate motions

As mentioned, the dielectric j3 peak is related to carbonate motions however, it is important to check whether the adjacent phenyl groups are involved or not in such motions. Concerning this feature, it is interesting to consider the dielectric behaviour of TMBPA-PC. The temperature dependence of the... 

This result clearly shows the intramolecular cooperativity associated with the carbonate motion. 

The overlap of the carbonate carbon and the non-protonated aromatic carbon lines in MAS-CP 13C NMR does not allow one to study the carbonate motions in BPA-PC. 

From the various experimental investigations, it is clear that carbonate motions, as well as phenyl ring motions, are involved in the mechanical p transition of BPA-PC. The intermolecular contribution has been evidenced by several authors and the cooperative character of the motions has been pointed out. However, neither of the considered techniques can provide detailed information about the nature of intra- or inter-cooperativity occurring in the glassy state. 

Although the symmetry selection rules allowed any vibration of species E20 of the covering D6h group to induce intensity in the Eiu-Aig transition Ingold had confirmed that one only of the four motions of that symmetry (606 cm 1 in the ground state) was effective. The second predominantly skeletal carbon motion at 1596 cm 1 barely appeared. 

We call the correlation time it is equal to 1/6 Dj, where Dj is the rotational diffusion coefficient. The correlation time increases with increasing molecular size and with increasing solvent viscosity, equation Bl.13.11 and equation B 1.13.12 describe the rotational Brownian motion of a rigid sphere in a continuous and isotropic medium. With the Lorentzian spectral densities of equation B 1.13.12. it is simple to calculate the relevant transition probabilities. In this way, we can use e.g. equation B 1.13.5 to obtain for a carbon-13... 

Small molecules in low viscosity solutions have, typically, rotational correlation times of a few tens of picoseconds, which means that the extreme narrowing conditions usually prevail. As a consequence, the interpretation of certain relaxation parameters, such as carbon-13 and NOE for proton-bearing carbons, is very simple. Basically, tlie DCC for a directly bonded CH pair can be assumed to be known and the experiments yield a value of the correlation time, t. One interesting application of the measurement of is to follow its variation with the site in the molecule (motional anisotropy), with temperature (the correlation... 

Kovacs H, Bagley S and Kowalewski J 1989 Motional properties of two disaccharides in solutions as studied by carbon-13 relaxation and NOE outside of the extreme narrowing region J. Magn. Reson. 85 530 1... 

Allyl Bromide. Introduce into a 1-litre three-necked flask 250 g. (169 ml.) of 48 per cent, hydrobromic acid and then 75 g. (40-5 ml.) of concentrated sulphuric acid in portions, with shaking Anally add 58 g. (68 ml.) of pure allyl alcohol (Section 111,140). Fit the flask with a separatory funnel, a mechanical stirrer and an efficient condenser (preferably of the double surface type) set for downward distillation connect the flask to the condenser by a wide (6-8 mm.) bent tube. Place 75 g. (40 5 ml.) of concentrated sulphuric acid in the separatory funnel, set the stirrer in motion, and allow the acid to flow slowly into the warm solution. The allyl bromide will distil over (< 30 minutes). Wash the distillate with 5 per cent, sodium carbonate solution, followed by water, dry over anhydrous calcium chloride, and distil from a Claisen flask with a fractionating side arm or through a short column. The yield of allyl bromide, b.p. 69-72°, is 112 g. There is a small high-boiling fraction containing propylene dibromide. 

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La203 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. 

---