Solid negative substitution

Carbocations are intermediates in several kinds of reactions. The more stable ones have been prepared in solution and in some cases even as solid salts, and X-ray crystallographic structures have been obtained in some cases. An isolable dioxa-stabilized pentadienylium ion was isolated and its structure was determined by h, C NMR, mass spectrometry (MS), and IR. A P-fluoro substituted 4-methoxy-phenethyl cation has been observed directly by laser flash photolysis. In solution, the carbocation may be free (this is more likely in polar solvents, in which it is solvated) or it may exist as an ion pair, which means that it is closely associated with a negative ion, called a counterion or gegenion. Ion pairs are more likely in nonpolar solvents. 

In this way and by numerical evaluation, Driessens (2) proved that the experimental activities could be explained on the basis of substitutional disorder, according to Equation (27), within the limits of experimental error. It seems, therefore, that measurements of distribution coefficients and the resulting activities calculated by the method of Kirgintsev and Trushnikova (16) do not distinguish between the regular character of solid solutions and the possibility of substitional disorder. However, the latter can be discerned by X-ray or neutron diffraction or by NMR or magnetic measurements. It can be shown that substitutional disorder always results in negative values of the interaction parameter W due to the fact that... 

Solution When the two solid surfaces are far apart (d = oo), the free end of each adsorbed rod has access to sites, with = 2itL2 and L the length of the rod. When the separation is such that the second surface cuts off access to some of these sites, the number of accessible sites becomes The subscript here indicates a separation less than some critical distance that is the threshold for interaction. The exact form of and the critical separation at which it begins to apply depends on whether one or both surfaces carry the adsorbed rods. The fraction of the area of the hemisphere that remains accessible to the free ends of the rods could be calculated from geometrical considerations. Using these Q values as substitutions in Equation (3.46), we obtain ASR = kB In (fia/fic). Since ASR is negative. This gives the effect per... 

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