Phenols ring substitution

An old name for benzene was phene and its hydroxyl derivative came to be called phe nol This like many other entrenched common names is an acceptable lUPAC name Likewise o m and p cresol are acceptable names for the various ring substituted hydroxyl derivatives of toluene More highly substituted compounds are named as deriv atives of phenol Numbering of the ring begins at the hydroxyl substituted carbon and proceeds m the direction that gives the lower number to the next substituted carbon Sub stituents are cited m alphabetical order... 

Hydroxyl Group. Reactions of the phenohc hydroxyl group iaclude the formation of salts, esters, and ethers. The sodium salt of the hydroxyl group is alkylated readily by an alkyl hahde (WiUiamson ether synthesis). Normally, only alkylation of the hydroxyl is observed. However, phenolate ions are ambident nucleophiles and under certain conditions, ring alkylation can also occur. Proper choice of reaction conditions can produce essentially exclusive substitution. Polar solvents favor formation of the ether nonpolar solvents favor ring substitution. 

The effect substitution on the phenolic ring has on activity has been the subject of several studies (11—13). Hindering the phenolic hydroxyl group with at least one bulky alkyl group ia the ortho position appears necessary for high antioxidant activity. Neatly all commercial antioxidants are hindered ia this manner. Steric hindrance decreases the ability of a phenoxyl radical to abstract a hydrogen atom from the substrate and thus produces an alkyl radical (14) capable of initiating oxidation (eq. 18). 

Para substituted phenol ethers Ring substituted dihydroxj benzenes Cyclohexane alcohols Menthenols. ... 

Novolacs are prepared with an excess of phenol over formaldehyde under acidic conditions (Fig. 7.6). A methylene glycol is protonated by an acid from the reaction medium, which then releases water to form a hydroxymethylene cation (step 1 in Fig. 7.6). This ion hydroxyalkylates a phenol via electrophilic aromatic substitution. The rate-determining step of the sequence occurs in step 2 where a pair of electrons from the phenol ring attacks the electrophile forming a car-bocation intermediate. The methylol group of the hydroxymethylated phenol is unstable in the presence of acid and loses water readily to form a benzylic carbo-nium ion (step 3). This ion then reacts with another phenol to form a methylene bridge in another electrophilic aromatic substitution. This major process repeats until the formaldehyde is exhausted. 

C—H bonds. Phenol, mono-ortho, and di- and tri-substituted phenolic rings can be monitored between 814-831, 753-794, 820-855, and 912-917 cm-1, respectively. Para-substituted phenolic rings also absorb in the 820-855-cm 1 region. 

Resole syntheses entail substitution of formaldehyde (or formaldehyde derivatives) on phenolic ortho and para positions followed by methylol condensation reactions which form dimers and oligomers. Under basic conditions, pheno-late rings are the reactive species for electrophilic aromatic substitution reactions. A simplified mechanism is generally used to depict the formaldehyde substitution on the phenol rings (Fig. 7.21). It should be noted that this mechanism does not account for pH effects, the type of catalyst, or the formation of hemiformals. Mixtures of mono-, di-, and trihydroxymethyl-substituted phenols are produced. 

The synthesized CPMV-alkyne 42 was subjected to the CuAAC reaction with 38. Due to the strong fluorescence of the cycloaddition product 43 as low as 0.5 nM, it could be detected without the interference of starting materials. TMV was initially subjected to an electrophilic substitution reaction at the ortho-position of the phenol ring of tyrosine-139 residues with diazonium salts to insert the alkyne functionality, giving derivative 44 [100]. The sequential CuAAC reaction was achieved with greatest efficiency yielding compound 45, and it was found that the TMV remained intact and stable throughout the reaction. 

Suatoni, J. C., R. E. Snyder, and R. O. Clark (1961), "Voltammetric Studies of Phenol and Aniline Ring Substitution," Anal. Chem. 33, 1894-1897. 

The chemical character of a compound is not fundamentally altered by the introduction of a nitro-group. Thus the ring-substituted nitro-derivatives of the hydrocarbons are neutral compounds like the hydrocarbons themselves. If, however, a nitro-group enters a substance having, for instance, an acid character, then this character is thereby intensified the nitrophenols, for example, are more acidic than phenol. Correspondingly, the strength of bases is decreased by nitration the nitranilines are less basic than aniline. 

This is a simple procedure for the enzymatic resolution of a secondary amine. The acylating agent can be modified by altering the substitution on the phenol ring. This tuning of the reactivity and selectivity should allow other amines to be resolved using a similar approach. 

When Cl and MeO substituents are attached to the phenolic ring, the PFR may result in displacement of those substituents by the acyl moiety. An example of chlorine displacement has been given in Section I, whereas Scheme 10 shows the case of 2-methoxy-4-methylphenyl benzoate (26), where the reaction mixture contains 2-hydroxy-5-methylbenzophenone (27), a product of methoxy substim-tion [37]. Hageman also reported the substitution of MeO by acetyl in the photolysis of 4-methoxyphenyl acetate and related esters [32]. 

The process is reversible and therefore provides an easily visible method for measuring pH change in the range of 8.5-9.0. The ionisation reactions of sulfophthaleins follow a similar pathway. Substitution in the phenolic rings of the phthaleins and sulfophthaleins provides a variety of coloured dianions, which change colour over different ranges of pH (see section 1.4.2.1). 

Vinyltrimethylstannanes react with xenon difluoride in dichloromethane at room temperature in the presence of equimolar (or a 50 Vo excess) of silver trifluoromethanesulfonate and a catalytical (0.1 equiv) quantity of 2,6-di-/e/7-butyl-4-methylpyridine to form the corresponding vinyl fluorides in high to moderate yields.54 57 The substitution reaction is tolerant to various functional groups, such as ketones, esters, carbamates, ketals, ethers, phenol rings and tertiary alcohols. As byproducts corresponding alkenes have been detected due to pro-tiodestannylation. 

In phenol and substituted phenols the C—O bond has some doublebond character, as discussed in Section 8-3. This tends to cause the hydrogen atom io lie in the plane of the benzene ring. The phenol molecule can thus assume either of the two configurations... 

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