Hydroxyl groups, substitution with

Gallotannins are hydrolysable tannins with a polyol core (referring to a compound with multiple hydroxyl groups) substituted with 10-12 gallic acid residues. Gallotannins contain the characteristic raeto-depside bonds (1.91) between gallic acid residues. This bond is more labile than an aliphatic ester bond, and can be methanolyzed with a weak acid in methanol. In contrast, methanolysis of an aliphatic ester bond requires methanol with a strong mineral acid and heat. 

Poly(vinyl alcohol) readily reacts with a wide variety of Isocyanates In DMSO solution (Equation 1) to produce modified polymers that contain 10-100% of the original hydroxyl groups substituted with carbamate groups. The yields of such reactions are essentially quantitative. Similar results have been reported from other research groups (14-16). tinder these conditions, poly(vinyl alcohol) has been reacted with 3- and 4-chlorophenyl-Isocyanate (this study), phenyllsocyanate (12-14), methyl, ethyl. Isopropyl and 1-naphthyl Isocyanates (14) and methoxymethyllso-cyanate (15,16). The reaction of PVAl with phenyl, tolyl and 4-chlorophenyl Isocyanates In dlmethylacetamlde solutions has also been reported (17). 

The cholestane molecule may have hydroxyl groups substituted at 25 of its 27 carbon atoms (C-10 and C-13 excepted). Each of these carbon atoms is so situated that it renders its hydroxyl substituent(s) sterically and, more subtly, electronically unique with respect to each of the others. If the cholestane skeleton is maintained, each of the possible secondaiy hydroxyls may assume... 

The sodium salt of the cymene sulphonic acid is then fused with sodium hydroxide in the usual manner, and the hydroxyl group substituted for the sulphonic group. This gives l-methyl-3-hydroxy-4-isopropyl-benzene or thymol. 

Mixed pentaerythritol esters have also been described [50] that contain in their molecule hydroxyl groups substituted by organic acids, which possess nitro groups either in ester form or as C-nitro compounds joined with the acid, alongside simple nitrate ester groups. 

Fig. 18. The expected percentages of various labelled products of the dioldehydratase reaction using 25 as substrate. The calculation was based on the following facts and assumptions (1) The enzyme does not differentiate between the enantiotopic hydrogen positions (conclusion from experiments with species 17 and 18 shown in Fig. 14) (2) in the competition between vicinal hydrogen atoms there is an intramolecular kinetic deuterium isotope effect of 2.6 (Fig. 15) (3) this effect is 10 for geminal hydrogen atoms (4) the migrating hydroxyl group substitutes one of the hydrogen atoms in the vicinal position stereospecifi-cally (i.e., with inversion).

The effect of substituting agents at silicon atom in difunctional organocyclotetrasiloxanes on reac-tivity of haloid and hydroxyl groups interacting with a,ra-dichloro(dihydroxy)-dimethylsiloxanes was studied. Polycondensation of dichlorohexaorganocyclotetrasiloxanes were performed at room temperature in 70% solution of anhydrous toluene or benzene both with acceptor and without it. 

It has been observed that reactions of dibutylstannylene acetals of terminal 1,3-diols, or polyols having primary hydroxyl groups free, with t-butyldimethylsilyl chloride yield primary silyl ethers, even for such compounds as methyl a-D-mannopyranoside, where the expectation (see Table VI) for most reactions is for substitution to occur on a secondary oxygen atom.85 88 These observations probably arise from a very large kinetic preference for reaction with primary oxygen atoms, that is, ki2 and k]2 > k2 and K22, in Fig. 12, rather than a rearrangement from initially formed secondary silyl ethers. 

The theoretical nitrogen content for each fraction can be calculated (Table IX). The lignin component is based on 1.16 hydroxyl groups per 9-carbon unit (13). The value of 8.37% nitrogen for the theoretical nitrogen content of lignin, if all available hydroxyls were substituted with methyl isocyanate, was calculated as ... 

Monoacylglycerols consist of a single hydroxyl group substitution of the glycerol molecule with an acyl residue via an ester linkage (Figure 3.3). Three positional isomers are therefore possible for the substitution sn-l, the central carbon position sn-2, or the terminal carbon position sn-3. Unlike the sn-l and sn-3 isomers, the sn-2 isomer retains its molecular symmetry and is therefore nonchiral. 

Hydroxyl groups substituted at positions 2- and 4-(6-) of the pyrimidine nucleus exist mainly in the pyrimidone form [1-4]. The only true hydroxyl position on this ring system is position 5. This hydroxyl group is of phenolic character and all 5-hydroxypyrimidines give a positive (blue-violet coloration) test with ferric chloride. Because of the relative difficulty in synthesis of all but a few compounds, most 5-hydroxypyrimidines have not been extensively studied. 

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