<unk>  is a class of chemical reactions which result in an addition of hydrogen (H2) usually to unsaturated organic compounds.  Typical substrates include alkenes, alkynes, ketones, nitriles, and imines.  Most<unk> s involve the direct addition of diatomic hydrogen (H2) but some involve the alternative sources of hydrogen, not H2: these processes are called transfer<unk> s.  The reverse reaction, removal of hydrogen, is called dehydrogenation.
The classical example of a<unk>  is the addition of hydrogen on unsaturated bonds between carbon atoms, converting alkenes to alkanes. Numerous important applications are found in the petrochemical, pharmaceutical and food industries.  Health concerns associated with the<unk>  of unsaturated fats to produce saturated fats and trans fats is an important aspect of current consumer awareness.<unk>  differs from protonation or hydride addition (e.g. use of sodium borohydride): in<unk> , the products have the same charge as the reactants.
Hydrogenation
Hydrolysis
Carboxylation
Hydroxylation
Alkylation
Electrolysis
Autoxidation
Deprotonation