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Electrophilic Addition

Alkynes are even richer in electrons than alkenes. That's why alkynes undergo electrophilic addition even more easily than alkenes.

Addition of hydrogen halides

Addition of excess HBr to a terminal alkyne: two successive Markovnikov additions give the geminal dihalide

Addition of water

Hydration of a terminal alkyne with H₂O/H⁺ and HgSO₄: the more substituted alkenyl carbocation takes up water and the enol formed tautomerizes to the methyl ketone

Addition of boranes

Hydroboration of a terminal alkyne with dicyclohexylborane and oxidation with H₂O₂/HO⁻: the anti-Markovnikov enol tautomerizes to the aldehyde