The acidity of a hydrogen atom is related to the stability of the conjugate base formed after the hydrogen atom is removed. In the case of 1-butyne, the conjugate base is a resonance-stabilized carbanion. The negative charge in the carbanion can be delocalized over both of the triple bond carbons, which helps to stabilize the species.

In contrast, the conjugate base of 2-butyne is not as stable. The negative charge in the carbanion cannot be delocalized as effectively over the two triple bond carbons, which means that the species is less stable. As a result, 2-butyne is not acidic enough to donate a proton in typical acid-base reactions.

The difference in acidity between 1-butyne and 2-butyne can be seen in their pKa values. The pKa of 1-butyne is 23, while the pKa of 2-butyne is 26. This means that 1-butyne is a stronger acid than 2-butyne.

The acidity of alkynes can also be affected by the presence of other functional groups. For example, the presence of a carbonyl group near the alkyne can increase the acidity of the alkyne. This is because the carbonyl group can withdraw electrons from the alkyne, which makes the hydrogen atoms on the alkyne more acidic.