Nonsubstituted phenol

Nonsubstituted phenols Methyl-phenols Ch loro-phenols Nitro-phenols... 

Equation (7.15) was obtained from the data of rate constants for the reaction of tert-butyloxyradical with /jora-substituted phenols [46,47], It was also assumed that the preexponent of the rate constant for reaction (12) is weakly dependent on the molecular structure of the ortAo-nonsubstituted phenol. The value of k 2 was calculated from (7.20) for />oh= 364.4 kJ/mol, corresponding to the dissociation energy of the OH-bond in /jara-methylphenol [11]. 

For the reaction of the ethylbenzene oxidation inhibited by BHT the negative contribution of steps with the participation of the quinolide peroxides formed just by the transformations of ortAo-substituted phenols is characteristic. In the case of applying BHT, as a rule, a substantial negative contribution is introduced by the reaction of the phenoxyl radical with the hydroperoxide, the reverse reaction of the peroxyl radical with BHT. At first sight this result seems to be imexpected, so far as the rate constant of the reaction between the ortho-substituted phenoxyl radical and the hydroperoxide is significantly smaller than that of the similar reaction with the ortAo-nonsubstituted phenoxyl radicals. As numerical experiments have shown, the reason is that imlike the ori/ o-nonsubstituted phenols, in the case of the ortAo-substituted phenols the reaction occurs under a kinetic mode with relatively high predominance in the concentration of the phenoxyl radicals over the peroxyl ones. In other words, in the case of BHT the role of the reaction between the phenoxyl radical and the hydroperoxide increases at the expense of the concentration factor. 

Properties of homologues of phenols with two tert. butyl groups in an ortho-positions are bound to influence of the next atoms of hydrogen tert. butyl groups on reactivity of phenolic hydroxyl and geometric parameters of an aromatic cycle. This influence causes appearance of antioxidative properties which are characterized by value k [15]. Operator Hartrii-Fo-cks with an odd number of electrons considers a spin component that is used at calculation energy formations phenoxy radicals. Calculations of structure nonsubstituted phenol (1) are carried out and 2-10 4-Z-replased -2,6-di-reA r.butylphenols in approach PM3 and PM6 too (Eq. (1)). 

Silicon bound to a phenyl group can also influence the bond system by additional (p- -d) back donation from carbon to silicon. In agreement with this model, p-trimethylsilyl-substituted benzoic acid shows a greater acidity than expected from inductive effects. Furthermore, p-trimethylsilyl phenol exhibits a greater acidity than phenol itself, and p-trimethylsilyl aniline shows a decreased basicity as compared with that of the nonsubstituted compound. This behaviour can be described by the following resonance structures [Eqs. (4) and (5)] ... 

The condensation reactions become important in a later stage when the concentration of the substituted phenols has increased. These reactions can occur in two different modes, as in the two examples sketched in Fig. 2.10 namely, the substituted methylol groups can react either with a nonsubstituted (free) position of a different aromatic ring (a) or with a second methylol group (b). 

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