In chemistry a<unk>  is a solvent that has a hydrogen atom bound to an oxygen as in a hydroxyl group or a nitrogen as in an amine group.  More generally, any molecular solvent which contains dissociable H+, such as hydrogen fluoride, is called a<unk> .  The molecules of such solvents can donate an H+ (proton). Conversely,<unk> s cannot donate hydrogen.
Common characteristics of<unk> s:
solvents display hydrogen bonding
solvents have an acidic hydrogen (although they may be very weak acids)
solvents are able to stabilize ions
cations by unshared free electron pairs
anions by hydrogen bonding
cations by unshared free electron pairs
anions by hydrogen bonding
Examples are water, methanol, ethanol, formic acid, hydrogen fluoride and ammonia.
Polar<unk> s are solvents that share ion dissolving power with<unk> s but lack an acidic hydrogen. These solvents generally have high dielectric constants and high polarity.
Examples are dimethyl sulfoxide, dimethylformamide, dioxane and hexamethylphosphorotriamide, tetrahydrofuran.
Polar<unk> s are favorable for SN1 reactions, while polar<unk> s are favorable for SN2 reactions. Apart from solvent effects, polar<unk> s may also be essential for reactions which use strong bases, such as reactions involving Grignard reagents or n-butyllithium. If a<unk>  were to be used, the reagent would be consumed by a side reaction with the solvent.
Protic solvent
Inorganic nonaqueous solvent
Generic drug
Detergent
Bath salts
Inhalant
Phytochemical
Food additive