Hydroxyl groups adjacent

Benzylidene dioxolane derivatives, under the same conditions except for the presence of water, give rise to monohydroxy benzoates with an equatorial hydroxyl group adjacent to an axial O-benzoyl group (Scheme 4) [20],... 

The enhanced reactivity of the 2-hydroxyl as compared to other secondary hydroxyl groups has been noted primarily in reactions requiring alkaline media. This effect is probably a result of the greater acidity of hydroxyl groups adjacent to a carbonyl or a potential carbonyl group. 

When, in a sugar, a hydroxyl group adjacent to a carbonyl group is inverted, as by D-en/f/iro-pentulose 5-phosphate 3-epimerase,48 complete exchange with solvent of the hydrogen on the epimerized carbon atom is usually observed, indicating an enediol mechanism. 

Dimorphotheca The seed of Dimorphotheca pluvialis is not very rich in oil (13-28%, typically about 20%), but it contains an unusual Cjg hydroxy fatty acid ( 60%) with hydroxyl group adjacent (allylic) to a conjugated diene system. This is very unstable and easily dehydrates to a mixture of conjugated 18 3 acids (105). 

Tertiary alcohols are resistant to oxidation. rcr -Butyl alcohol is frequently used as a solvent in oxidations. However, some tertiary alcohols are converted into tertiary hydroperoxides on treatment with hydrogen peroxide in sulfuric acid [177, 179]. Dimethylphenylcarbinol added to a mixture of 87% hydrogen peroxide and sulfuric acid at a temperature below 0 °C gives a 94% yield of cumyl hydroperoxide after 3.5 h [777]. Similarly, acetylenic alcohols with the tertiary hydroxyl group adjacent to the triple bonds are converted into the corresponding hydroperoxides in high yields [179] (equation 272). 

The pentose sugars, ribose and xylose also yield the pentitols on reduction under similar conditions [29]. In these cases a by-product is the 2-deoxypolyol formed by reductive elimination of the hydroxyl group adjacent to the carbonyl function. This reaction predominates during the reduction of D-xylose in solution at pH 9 at amalgamated lead when 2-deoxy-D-xylitol (III) is formed in 62% yield [30]. 

The inhibitory effect of an extra hydroxyl group adjacent to a site of metabolism has been used to provide evidence for a putative biosynthetic intermediate. The kaurenolide lactones are formed from ent-kaur-6,16-dien-19-oic acid (10.25) by G. fujikuroi. It was suggested that a 6,7-epoxide was formed first and that this underwent a diaxial opening with participation of the... 

However, all the free hydroxyl groups of cellulose are weakly ionizable, as is shown by the complete exchange of hydrogen for deuterium which takes place when it is immersed in deuterium oxide. The more acidic properties of the C2 hydroxyl group might be attributable to a permanent polarization of hydroxyl groups adjacent to a carbonyl or potential carbonyl group (see p. 293). 

Synthesis of heterocycles [before references]. Hendrickson et al developed a useful general synthesis of heterocycles in which the key step is a Michael addition of the reagent to a substrate of a variety of types having an amino, mercaptan, or hydroxyl group adjacent to an electrophilic center. An example is the reaction of a-aminopropiophenone hydrochloride, and sodium acetate to liberate the amine (1), with dimethyl acetylenedicarboxylate in refluxing methanol. Sodium chloride... 

Both sonicated and imsonicated dispersions of dipalmitoylglycerophosphocholine and cholesterol in water have been studied by proton nmr spectroscopy. The observed line widths provide a useful indication of the mobility of the system. Analysis of the relative intensities of the observed signals locates the steroid between the phospholipid hydrocarbon chains of the bilayer with the steroid hydroxyl group adjacent to the phosphate groups of the phosphatidylcholines [34]. The number of hydrocarbon chain gauche-trans isomers of the phosphohpid are reduced by the presence of the cholesterol molecules. 

Some very tentative conclusions have been drawn as to the structural features of isopyro-a-oxodelphinine (though it is impossible to extend these directly to pyro-a-oxodelphinine). Since chromic acid attack occurs readily only on isopyro-a-oxodelphonine (i.e., after saponification of the. benzoate group), it is suggested that the benzoyl group is attached to a secondary hydroxyl group, adjacent to a tertiary hydroxyl (see part-formulas above). 

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