ABSTRACT

The terminal and internal alkynes undergo acid catalyzed hydration to yield enol as an intermediate, which is in tautomeric equilibrium with its corresponding aldehyde or ketone, respectively. The 1-alkyne is referred to as the terminal alkyne, while the triple bond in any other position is referred to as internal alkynes. Similar to alkenes, the numbering scheme in alkynes gives the smallest number to the carbon of the triple bond. Alkynes also react with hydrogen halides from both polar and radical mechanism. The reaction hydrochlorination of phenylprop-1-yne passes through the p complex and the transition state where chloride ion is at the same side with respect to the added hydrogen atom in the alkyne to form the syn product. Since the triple CC bond is stronger than double CC bond, the former has smaller CC bond length than the latter.