Alkenes and some alkynes also undergo polymerization, alkene metathesis, and alkyne metathesis. Ketones containing alkene and alkyne units are often called unsaturated ketones. Dihydroxylation of alkene produces diol, and dihydroxylation of alkyne produces vicinal dicarbonyl. In alkene radicals proton abstraction to an alkyne is preferred. Using an alkyne instead of an alkene yields an enol, which tautomerizes into a ketone. Khand reactions, where the starting material contains both the alkene and alkyne moieties, are possible. For instance, semihydrogenation of an alkyne may form an alkene. Molecules called ene-diynes feature a ring containing an alkene ("ene") between two alkyne groups ("diyne"). It is composed of both alkyne and alkene groups and is the simplest enyne. Such complexes occur also in metal catalyzed reactions of alkynes such as alkyne trimerization. Non-carbon reagents also undergo cyclization, e.g. Azide alkyne Huisgen cycloaddition to give triazoles. The hydrohalogenation of alkyne is much slower than the alkene. BSA contains a thiol group at Cys-34 which is functionalized with an alkyne group. Usually two equivalents of sodium amide yields the desired alkyne. Oxidative demetallation gives the desired alkylated alkyne.