Two moles of a very strong base, such as butyl lithium `(BuLi)`, convert an alkyne into dianion by the removal of the terminal H and a propargylic H.
Propargylic H is acidic due to resonance stabilisation (extended delocalisation) of the negative charge, as shown:
Moreover, due to the `sp` hybrid character of triple-bonded C, alkyne group `(-C-=C-R)` is EWG (electron withdrawing) and therefore is acid strengthening.
