Polar protic and aprotic solvents

Water, alcohols, and carboxylic acids are polar proticsolvents able to form hydrogen bonds (hydroxylicsolvents). They solvate both cations and anions well. Anucleophilic reagent such as bromide ion must beaccompanied by a cation, say, the sodium ion, andhydroxylic solvents dissolve salts such as NaBr byhydrogen bonding to the anion and electron donation tothe cation. This is solvation by a polar protic solvent.These solvents do not ‘ionize’ the salt, which alreadyexists in the solid state as ions; they separate andsolvate the ions already present.

Polar aprotic solvents, on the other hand, have dipolemoments and are still able to solvate cations by electrondonation from an oxygen atom, but they lack the ability toform hydrogen bonds because any hydrogen atoms theymay have are on carbon. Examples include DMF andDMSO (dimethyl sulfoxide).







Source: organic chemistry, Clayden