Q.Convert: 3-Methylbut-1-yne into 3-Methylbutan-2-one.

Step 1. Draw the starting terminal alkyne. 3-Methylbut-1-yne is HC(triple bond)C-CH(CH3)-CH3 -- a terminal triple bond (C1-triple bond-C2) with a methyl branch on C3.

Step 2. Apply the section 15.3.4 hydration method. Treating a terminal alkyne with water in the presence of 40% H2SO4 and 1% HgSO4 adds water by Markovnikov's rule, putting the -OH on the MORE substituted (internal) alkyne carbon, C2, not the terminal C1.

Step 3. Form the enol, then tautomerise. This gives an unstable enol, H2C=C(OH)-CH(CH3)-CH3, which instantly tautomerises (as with every other alkyne hydration in section 15.3.4) to the far more stable carbonyl form: the C=C-OH becomes C-C=O, shifting the double bond and moving a hydrogen from oxygen to the adjacent carbon. …

Applying Markovnikov-selective, Hg2+-catalysed hydration of a terminal alkyne, then tautomerising t …

• Adding water the wrong way round (anti-Markovnikov), which would give an aldehyde on C1 instead of the required ketone on C2. …