Cyclodextrins hydrogen bonding

Ihb = 1, whereas Ihb = 0 when it is inert to hydrogen bonding. Since —AG,° is proportional to log 1/Kd, where Kd is the dissociation constant of a cyclodextrin complex with a guest molecule, we can derive a quantitative structure-reactivity relationship as shown, for example, in Eq. 4 ... 

Only the hydrophobic and steric terms were involved in these equations. There are a few differences between these equations and the corresponding equations for cyclo-dextrin-substituted phenol systems. However, it is not necessarily required that the mechanism for complexation between cyclodextrin and phenyl acetates be the same as that for cyclodextrin-phenol systems. The kinetically determined Kj values are concerned only with productive forms of inclusion complexes. The productive forms may be similar in structure to the tetrahedral intermediates of the reactions. To attain such geometry, the penetration of substituents of phenyl acetates into the cyclodextrin cavity must be shallow, compared with the cases of the corresponding phenol systems, so that the hydrogen bonding between the substituents of phenyl acetates and the C-6 hydroxyl groups of cyclodextrin may be impossible. 

Kim YH, Cho DW, Yoon M, Kim D (1996) Observation of hydrogen-bonding effects on twisted intramolecular charge transfer of p-(N, N-diethylamino) benzoic acid in aqueous cyclodextrin solutions. J Phys Chem 100(39) 15670-15676... 

JOC3338, 2003OL3839>. The addition of ot-cyclodextrin (lequiv) increased the yield, but did not influence the translcis-selectivity <1996J(P1)1113>. The higher yield of 79 in aqueous medium was explained as a result of the hydrophobic effect on a reactant encapsulated in a cavity surrounded by a hydrogen-bonded network of water molecules <2001JOC3338>. 

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