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Boiling Point

One of the most important properties of alcohols is their ability to form hydrogen bonds. Since alcohols can form hydrogen bonds, they have very high boiling points. Consider the following comparative analysis to clarify this idea.
The boiling point of ethane (C2H6) is – 88.7 0 C.
The boiling point of propane (C3H8) is – 42.2 0 C.
The boiling point of ethanol (C2H5OH) is 78 0 C.


Note the drastic difference in their boiling points.

By the above comparison, it is clear that some extra forces (here mainly H bonds) are working to increase the boiling points of alcohols.


image\29157 ch 21 fig 21-1.png


Solubility in H2O

Low-molecular weight alcohols are soluble in water. The hydrogen bond formation plays a key role in the solubility of alcohols in water. In other words, hydrogen bonds enhance the solubility of alcohols in H2O. As the number of carbons increases, the solubility of alcohols decreases as they become more and more similar to hydrocarbons with longer and longer nonpolar hydrocarbon chains.

Acidity of Alcohols

Alcohols are weakly acidic. In fact, they are weaker in acidity than water. Alcohols have Ka values around 10–17.
Alcohols give off the acidic hydrogen to form alkoxide ions. Alkoxide ion is the conjugate base of alcohols and they are strong bases.

image\Ch 21 sec B, g2.png

Among alcohols, primary alcohols are the most acidic, and tertiary alcohols are the least acidic.

image\26181 ch 21.png

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