Doublet phenols

Diphenoxy-2-propanol (3) was prepared from phenol and epichlorohydrin (l-chloro-2,3-epoxypropane), as previously described,8 and recrystallized three times from 2-propanol to yield white crystals, m.p. 82-82.5°C. The nmr spectrum in CDC1- (Varian EM-390 spectrometer) exhibited resonances (in ppm (6) relative to tetramethylsilane) at 3.0 (1H, doublet,... 

The structure of hexacoordi nate anions 2 and 3 is in addition supported by the doublet due to the splitting of phosphorus by the methine proton of Rf = CH(CF3)2 group. There is no indication for formation of a hexacoordinate structure containing two ORf groups when an excess of phenol is present. Among two pairs of hexacoordinate isomeric structures 2, 3 and 5, 6, the 2 and 5 seems to be kinetically and 3, 6 thermodynamically controlled. 

The low-temperature H NMR spectra for calix[4]- and calix[5]arenes reveal that all four or five phenolic units are identical.225 This is compatible with a cone conformation with C4v and C5v symmetry, respectively.226,227 For calix[8]arenes the same pattern is interpreted by a / -symmetrical pleated loop conformation, with a regular up-and-down of the methylene bridges. Calix[7]arenes, however, show seven singlets for the OH protons and seven (overlapping pairs of doublets) for the methylene protons. This total lack of any symmetry element (C,) makes this conformation chiral.228... 

An interesting situation has been found for calix[6]arenes. The low temperature NMR spectrum of r-butylcalix[6]arene shows three singlets for OH and r-Bu and three pairs of doublets for the Ar-CH2-Ar groups. This means that a symmetry plane, a twofold axis, or an inversion center must be present. A calix[6]arene consisting of two different phenolic units in alternating sequence (116) has by constitution a threefold axis. Due to this mismatch of symmetry elements it must be chiral (C,) at low temperature, which has been found in fact for 116.229 In addition, the authors conclude that the direction of the cyclic array of OH-OH hydrogen bonds (clockwise or... 

Using the 830/850 cm doublet as a measure of the negative state of phenolic oxygen and of the tyrosine environment. Van Dael et al. (1987) studied the effect of low pH on bovine a-lactalbumin Tyr groups. They also examined the stabilizing role of Ca(II) and Na(I) on the structure and the change in state of Trp residues as the molecule unfolds. 

Br, respectively. We think that this is a satisfactory explanation of why the cis-trans voh doublet in 0-FC6H4OH was not observed in CCI4. Second, the solvent strongly stabilizes the trans form so that the cis-trans gap cis—trans fnho appears to be equal to 3.4, 2.8 and 2.0 kl moC for F, Cl and Br, respectively. This straightforwardly implies an increase in the equilibrium constants k is, rans in series of F, Cl and Br equal to 0.25, 0.33 and 0.45, respectively with respect to that in the parent phenol. Third, the solvent reduces the cis-trans barrier to 11.8, 11.4 and 11.7 kImoG for F, Cl and Br, respectively. Altogether, we may conclude that even a rather simple modelling of solvent is able to resolve the aforementioned controversial state of affairs in the orf/zo-X-substituted phenols. 

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