The major proeduct of the following reaction is · ABC26OR0536
Subject: Organic Chemistry · Chapter: Organic Synthesis · Topic: Organic Synthesis – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Easy
The major proeduct of the following reaction is 
(a)
(b)
(c)
(d)
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Na/liq. NH3 reduces an internal alkyne to the trans (E)-alkene. Oct-4-yne therefore gives (E)-oct-4-ene, which is option (c). Option (d) is the cis isomer (the Lindlar product).
Explanation
Na in liquid NH₃ reduces an internal alkyne by a dissolving-metal mechanism: electron transfer gives a radical anion, protonation gives a vinyl radical that adopts the less hindered trans geometry, and a second electron plus protonation gives the alkene. Oct-4-yne therefore gives (E)-oct-4-ene. (d) is the cis alkene, which needs H₂/Lindlar; (a) and (b) are terminal isomers that are not formed. Answer: (c).
Study loop for Organic Synthesis