Bonding in alcohols and phenols

Figure 17.1 Hydrogen-bonding in alcohols and phenols. A weak attraction between a positively polarized OH hydrogen and a negatively polarized oxygen holds molecules together. The electrostatic potential map of methanol shows the positively polarized O-H hydrogen (blue) and the negatively polarized oxygen (red).

H hydrogen bonding in alcohols and phenols 3200-3600 strong, broad... 

The several detailed infrared studies of hydrogen bonding in alcohols and phenols are exemplified by the work of Stuart and Sutherland (1956), Lippincott and Schroeder (1955, 1956), " Jakobsen and Brasch (1965), and Lake and Thompson (1966). Investigators write about monomers, dimers, polymers, proton donors, proton acceptors, and free hydroxyl, but without reference to the formation of ions. 

The -OH group in alcohols and phenols is involved in intermolecular hydrogen bonding as shown below ... 

Bromine trifluoride has found application in the conversion of (methylsulfanyl)thiocar-bonyl groups, bonded to carbon atoms in aromatic rings, oxygen atoms in alcohols and phenols, or to the phthalimide nitrogen atom, into trifluoromethyl groups.125... 

Since the hydroxyl group is present in alcohols and phenols, these compounds are polar. The polarity of the hydroxyl group, coupled with its ability to form hydrogen bonds, enables many alcohols and phenols to mix with water. Since these compounds also contain nonpolar portions, they show additional solubility in many organic solvents, such as dichloromethane and diethyl ether. 

This experiment describes a characterization analysis in which the degree of association, equilibrium constant, and hydrogen bond energy are measured for benzyl alcohol and phenol in CCI4. 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

The triaLkoxy(aryloxy)boranes are typically monomeric, soluble in most organic solvents, and dissolve in water with hydrolysis to form boric acid and the corresponding alcohol and phenol. Although the rate of hydrolysis is usually very fast, it is dependent on the bulk of the alkyl or aryl substituent groups bonded to the boron atom. Secondary and tertiary alkyl esters are generally more stable than the primary alkyl esters. The boron atom in these compounds is in a trigonal coplanar state with bond hybridization. A vacantp orbital exists along the threefold axis perpendicular to the BO plane. 

Alcohols and phenols have nearly the same geometry around the oxygen atom as water. The R-O—H bond angle has an approximately tetrahedral value (109° in methanol, for example), and the oxygen atom is sp3-hybridized. 

Examples of hydrogen-bonding-promoted Diels-Alder reactions obtained by using alcoholic and phenolic solvents are illustrated in Section 6.2.4. 

In base-catalyzed addition to triple bonds, the rate falls in going from a primary to a tertiary alcohol, and phenols require more severe conditions. Other catalysts, namely, BF3 and mercuric salts, have also been used in addition of ROH to triple bonds. 

Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules as shown. The solubility decreases with increase in size of alkyl/aryl (hydro-phobic) groups. Several of the lower molecular mass alcohols are miscible with water in all proportions. 

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