Properties of Alcohols and Phenols

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. 

Another similarity with water is that alcohols and phenols are both weakly basic and weaJkly acidic. As weak bases, they are reversibly protonated by strong acids to yield oxonium ions, TOFty.  

As weak acids, they dissociate slightly in dilute aqueous solution by-donating a proton to water, generating H O+ and an alkoxide ion, RO-, or a phenoxide ion, ArO-. 

Recall from the earlier discussion of acidity in Sections 2.7 through 2.11 that the strength of any acid HA in water can be expressed by an acidity constant, Ka. 

Compounds with a smaller/C., and larger pKa are less acidic, whereas compounds with a larger/Ca and smaller pl a are more acidic. As shown by the data in Table 17.1, simple alcohols like methanol and ethanol are about as acidic as water but substituent groups can have a significant effect, tert-Butyl alcohol is a weaker acid, for instance, and 2,2,2-trifluoroethanol is stronger. Phenols and thiols, the sulfur analogs of alcohols, are substantially more acidic than water. 

Draw structures corresponding to the following lUPAC names  

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Alcohols and phenols eonsist of two parts, an alkyl/aiyl group and a hydrojQTl group. The properties of alcohols and phenols are ehiefly due to the hydrojQTl group. The nature of alkyl and aiyl groups simply modify these properties. 

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