Alcohols OH group

Polyethylene glycol 400 compounds with alcoholic OH groups 20 to 25-fold dipping solution, 10% in methanol [269]... 

Does the sample contain a substance with a carbonyl group or one that has been produced by oxidation of an alcoholic OH group ... 

R CO2 H -I- H2 O i CO2 + H3 O " In contrast, the hydrogen atom In the — OH group of an alcohol is not thought to undergo this reaction. A research chemist claims that this is incorrect, and that rapid exchange of H atoms occurs between alcoholic — OH groups and water molecules. Describe experiments that would test this claim. 

Secondaiy alcohol 15b presumably is isomerized to enol 28, but at temperatures of 70°C the laber is quickly converted to the most stable keto form (16b), the observed product. Interesbngly, silylation of the alcohol (29) allows for a mild and complete isomerizabon to ( )-30 at room temperature, confirming that an alcohol OH group somehow slows the first isomerizabon step. However, the alcohol... 

Conveniently prepared by the method here described, diazomethane is much used in scientific work, since it enables valuable acids and phenols to be elegantly and smoothly methylated. Alcoholic OH-groups are practically never attacked by diazomethane, nor are amines affected. 

The acidity of organic ligands is enhanced by coordination with the oxide surface, i.e. the surface promotes deprotonation of the functional groups (COOH or OH). Such ligands, therefore, adsorb on the surface at a pH 2-3 units lower than that at which complexation with Fe in solution would occur (Kummert and Stumm, 1980). An example of this is the deprotonation of the alcoholic OH group of tartaric acid upon adsorption on the goethite surface (Cornell and Schindler, 1980). The appropriate reaction for the acid in water is. 

The reaction of 14 may remind one of the well-established reaction mechanism for chymotrypsin (Fig. 5) (20). By comparing the acyl-trans-fer reaction of complex 14 with that of chymotrypsin 17, we find that the alcoholic nucleophiles in 14 and 17 are activated by Zn11—OH- and imidazole (in a triad), respectively. Several common features should be pointed out (i) Both reactions proceed via two-step reaction (i.e., double displacement), (ii) The basicity of Zn11—OH (pKa = 7.7) is somewhat similar to that of imidazole (plfa = ca. 7). (iii) The initial acyl-transfer reactions to alcoholic OH groups are rate determining, (iv) In NA hydrolysis with chymotrypsin, the pH dependence of both the acylation (17 — 18) and the deacylation (19 — 17) steps point to the involvement of a general base or nucleophile with a kinetically revealed piFCa value of ca. 7. A major difference here is that while the... 

However, essentially only one of them—namely, B—undergoes a nucleophilic backside attack by the hydroxy group. The brominated tetrahydrofuran D is produced via the oxonium ion C. An analogous intramolecular backside reaction by the alcoholic OH group in the bromonium ion iso-B is energetically disfavored and hardly observed. The result is that the bromonium ion iso-B can revert to the starting material A, whereby the overall reaction takes place almost exclusively via the more reactive bromonium ion B. 

Multistep synthesis problems are useful for exercising your knowledge of organic reactions, and in Chapter 8 we illustrated a systematic approach to synthesis. Now we apply this approach to a fairly difficult problem emphasizing alkyne chemistry. The compound to be synthesized is cA-2-methylhex-4-en-3-ol. (The 3-ol means there is an alcohol —OH group on C3.)... 

The proposed mechanism for this reaction is shown in Scheme 30. Coordination of the alcohol OH group to the Pd center causes deprotonation to produce the alkoxide-coordinated species. CO insertion produces the alkoxyacyl species, which reacts with the alkyne group to produce the cyclized vinyl-Pd species, which is then protonated off the Pd center. 

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