Shielding ratio

The Debye-Bueche theory, on the other hand, considers the partially draining coil as a sphere that is more or less permeable, within which a number of smaller beads is homogeneously distributed. The beads correspond to the monomeric units. The drag which one bead produces on the others is calculated, and this resistance is then expressed in terms of a length L, which corresponds to the distance from the surface of the sphere to where the flow rate of the solvent is reduced to 1 /e times what it is at the surface of this sphere. The shielding ratio, or shielding factor, is given by... 

C shielding ratio in the theory of random coils E partition function n osmotic pressure p density... 

The relationship between g and g is given by Eq. 7, where e is known as the viscosity shielding ratio ... 

Here, a is the exponent in the Mark-Houwink relationship ([ ] = AM ). As results from the mass method are also dependent upon the value of the viscosity shielding ratio, the same caveat expressed in the previous paragraph applies. 

According to this model, intrinsic viscosity depends not only on the molecular weight but also on the specific volume of the macromolecule and the shielding ratio, de Gennes considered this a model of porous sponge with uniform density. The monomers inside the sponge are screened from the flow. Only those on the surface are subject to friction. 

Calculate the root-mean-square end-to-end distance for a polystyrene with molecular weight 2 x 10 in benzene with an intrinsic viscosity of 107 mL/g. According to Debye and Bueche s analysis, the shielding ratio is in the vicinity of 0.836 with a = 3.92 (Debye and Bueche, 1948). 

Annulene satisfies the Huckel (4n+2) tt electron rule for aromaticity and many of its proper ties indicate aromaticity (Section 11 20) As shown in Figure 13 10a [18]annulene contains two different kinds of protons 12 he on the ring s periphery ( out side ) and 6 reside near the middle of the molecule ( inside ) The 2 1 ratio of outside/inside protons makes it easy to assign the signals in the NMR spectrum The outside protons have a chemical shift 8 of 9 3 ppm which makes them even less shielded than those of benzene The six inside protons on the... 

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