Find out the major products from the following reactions:

Step 1: Oxymercuration-demercuration (Path 1): Markovnikov addition

$\ce{Hg(OAc)2/H2O}$ followed by $\ce{NaBH4}$:

• $\ce{Hg(OAc)2}$ acts as an electrophile; mercurinium ion forms.
• Water attacks the more substituted (more electrophilic) carbon — Markovnikov selectivity.
• $\ce{NaBH4}$ reduces the C-Hg bond, replacing Hg with H.
• Product A = secondary/tertiary alcohol (Markovnikov product).

Key: no carbocation rearrangement (mercurinium ion mechanism is concerted-like).

Step 2: Hydroboration-oxidation (Path 2): Anti-Markovnikov addition

$(\ce{BH3})_2$ adds B to the terminal (less substituted) carbon (steric control). Oxidation replaces B with -OH at the same carbon.

• Product B = primary alcohol (anti-Markovnikov product).

Key comparison:

| Method | Regio | Stereo | Carbocation? | |---|---|---|---| | Oxymercuration | Markovnikov | Anti addition | No | | Hydroboration | Anti-Markovnikov | Syn addition | No |

Answer: A = Markovnikov (secondary OH), B = Anti-Markovnikov (primary OH) ✓

Key Points to Remember:

• Both methods avoid carbocation rearrangements.
• Oxymercuration = Markovnikov, anti addition, no rearrangement.
• Hydroboration = anti-Markovnikov, syn addition, no rearrangement.
• These two methods are complementary for regioselective alcohol synthesis.