Substituent Effects on the Acid Hydration of Acetylenes

Article abstract of DOI:10.1021/jo00344a006

The rates of hydration in aqueous sulfuric acid of 1-butyne, 2-butyne, 1-hexyne, 1-cyclopropylacetylene, and 1-butene are reported, together with rates in D2SO4 for the alkynes plus 3-hexyne.All of the compounds are proposed to react through the Ad_E2 mechanism of rate-limiting protonation on carbon.A general correlation of logk_H+(alkyne)/log k_H+(alkene) is observed, whose slope of 1.25 is a quantitative measure of the greater sensitivity to substituent effects of alkynes compared to alkenes in protonation.