Solute-Solvent Interactions in Ring Formation

In order to explain the experimental behavior found of X for PVP in the different mixtures, the polarizability was taken into account because of the methyl groups substituents of the aromatic ring. It is possible to And changes in the nature of the interactions between the polar solute, 2 - propanol, and the aromatic component in the binary mixtures and that these changes affect the X values. The importance of dipole - induced dipole interactions and steric factors in the formation of a molecular complex between a polar component and a non - polar aromatic solvent has been emphasized on the basis of NMR studies [111, 112], The molecular interactions in binary liquid mixtures have also been studied on the basis of viscosity measurements. The viscosity data have also been used by Yadava et al. [113,114] to obtain a value for the interchange energy (Wvisc) [115] This parameter can be estimated by the equation ... 

Much more recently, and with the advantage of sophisticated NMR techniques that have become available since the early 1970s, it has been shown that the spiro-3i/-pyrazole structure for 29a is incorrect. It is known that the outcome of diazocyclopentadiene addition to dimethyl acetylenedicarboxylate is dependent upon the five-membered ring substituents In the case at hand, tetraphenyldiazocyclopentadiene adds to the alkyne to give 29a as a labile product that rearranges under the reaction conditions to the 3H-indazole 30a (Scheme 3) 1,3-di-r-butyldiazocyclopentadiene behaves similarly l Thus in the formation of 31a at least, the spiropyrazole 29a is not the substrate and one must question the nature of the educt (29 versus 30) employed in cycloproparene synthesis by the spiro-3i/-pyrazole route. Nonetheless, there can be little doubt that spirocycle 29d is the substrate employed by Mataka and coworkers because, upon thermolysis, the corresponding indazole 30d was isolated. What must be noted here is that the thermal reaction did not provide any of the cyclopropa[/]phenanthrene 31d, but neither did independent photolysis of the isolable indazole 30d in benzene solution a 9,10-disubstituted phenanthrene is formed from diradical interaction with the solvent (equation 7). 

Fig. 1 Multiple molecular recognition Free metallocycle 1 is formed in dilute solution because of the enthalpy of formation of the Pd—N coordination bonds. When the solution is concentrated from 2-50 mM, the lability of these bonds allows the in situ formation of the interlocked catenane 2. This is driven by hydrophobic interactions to minimize the contact of the metallocycle cavities with the water solvent, the formation of 7t-stacking interactions between two such rings, and an entropic effect due to a decline in the number of species present in solution after interlocking.

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