The initial step of the oxidation of alkynes by permanganate has been studied by DFT (B3LYP/6-311+G(d,p)) calculations. The influence of electron-withdrawing as well as electron-donating substituents was explored. The singlet and triplet potential energy hypersurfaces (PES) for a concerted [3 + 2] and a stepwise [2 + 2] mechanism were investigated. The crossing point between the singlet and triplet PES has been identified. The reaction proceeds via a [3 + 2] mechanism on the singlet PES with free energy activation barriers (DeltaG(298)) between 18.4 and 28.9 kcal/mol, while the lowest lying identified state is a reactive triplet intermediate. Available experimental and computed data are in good agreement. For the [2 + 2] case a reaction on the triplet surface would be preferred over the singlet, but both pathways lay well above the [3 + 2] pathway.