Potassium chloride, structural change

An explanation not easily distinguishable from the one involving resonance with a carbonium ion structure in the transition state is that the reactive species is an ion pair in equilibrium with the covalent molecule. This is quite likely in a solvent insufficiently polar to cause dissociation of the ion pairs. Examples of second order nucleophilic displacements accelerated by the sort of structural change that would stabilize a carbonium ion are of fairly frequent occurrence. Allyl chloride reacts with potassium iodide in acetone at 50° seventy-nine times as fast as does -butyl chloride.209 Another example is the reaction of 3,4-epoxy-1 -butene with methoxide ion.210... 

The impurity concentration gradient theory assumes that the solution is more structured in the presence of a crystal. This increases the local supersaturation of the fluid near the crystal, which is the source of crystal nuclie. Changes in the structure of the solution near the crystal surface have been observed experimentally. Dissolved impurities in the solution are known to inhibit nucleation rates. Some of the impurities are incorporated into the crystal surface. Thus, a concentration gradient is formed that enhances the probability of nucleation. Experimental evidence of the theory was presented for the nucleation of potassium chloride in the presence of lead impurities. As expected, stirring the solution causes the impurity concentration gradient to disappear and hence, lower the nucleation rates (Denk 1970). 

When an aqueous solution of benzenediazonium chloride is added to a cold concentrated solution of potassium hydroxide, the unstable potassium diazo-tate, C(HjN NOK, is formed, and this when heated with alkali to 130° changes to the isomeric but far more stable potassium isodiazotate it is probable that these copipounds have the structures (A) and (B) respectively. 

In some crystals such rotation occurs at room temperature. One of the simplest examples is potassium cyanide, KON the structure is of the sodium chloride type (Fig. 127), and this can only mean that the CN ion is rotating it does not necessarily mean that all orientations are equally probable, but it does mean that frequent changes of orientation occur, such that the effective symmetry of the ion is the highest possible in the cubic system neither carbon nor nitrogen atoms occupy specific positions in the structure but are in effect spread over a number of positions. 

Aminopyrimidines. A number of substituted pyrimidines had a short-lived clinical usefulness and were developed because of their partial structural resemblance to the xanthines. Aminometradine and amisometradine (Figure 1.14) produce a sodium chloride diuresis together with a small potassium loss, but without changing the glomerular filtration rate. Presumably, therefore, they act upon reabsorptive processes in the tubule. However, since they are ineffective in patients with sodium depletion, it is unlikely they act on the distal tubule to block sodium channels [167,168]. Some substituted isocytosines are also... 

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