Predicting Relative Acidity of Alcohols

As we learned in Chapter 3, in order to determine the relative acidity of a compound, we must carefully assess the stabihty of its conjugate base. For example  

Therefore, in terms of acidity, alcohols will lie somewhere between amines and hydrogen halides  

The p/fa for most alcohols will fall in the range of 15-18. Remember, a low pKg. value means that a compound is fairly acidic, and a high value means that it is not very acidic. Compare the following p Ta values  

In Chapter 3, we learned how to analyze the four factors that stabilize a negative charge (ARIO). The I in ARIO stood for induction. We saw that neighboring halogens can withdraw electron density and stabilize the negative charge  

Therefore, the presence of halogens can lower the pA a value of an alcohol to around 14. In other words, the presence of a halogen will make the compound more acidic. The following two alcohols provide an interesting comparison  

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