Recall from our earlier discussion of acidity (Sections 2.7-2.11) that the strength of any acid HA in water can be expressed by an acidity constant, Ka:
Compounds with a smaller Ka(or smaller pKa) are more acidic. The data presented in Table 17.1 show that simple alcohols are about as acidic as water but that substituent groups can have a singnificant effect. For example, methanol and ethanol are similar to water in acidity, but tert-butyl alcohol is a weaker acid and 2,2,2-trifluoroethanol is stronger.