Borane adds rapidly to an alkyne just as it does to an alkene, and the resulting vinylic can be oxidized by H2O2 to yield an enol. Tautomerization then give either a ketone or an aldehyde, depending on the structure of the alkyne reactant. Hydroboration/oxidation of a terminal alkyne gives an aldehyde. Note that the relatively unhindered terminal alkyne undergoes two additions, giving a doubly hydroborated intermediate. Oxidation with H2O2 at pH 8 then replaces both boron atoms by oxygen and generates the aldehyde.