Organic Chemistry 1 · Alkyne transformations
Choose opposite alkene geometries
Conditions: Starting material: hex-3-yne. Compare poisoned-catalyst partial hydrogenation with dissolving-metal reduction; assume each is stopped at the alkene.
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The question
Which product mapping is standard?
Reveal the answer and explanation
Answer and explanation
Correct answer Poisoned catalyst → Z-hex-3-ene; dissolving metal → E-hex-3-ene
The first gives net syn H addition, while the second gives the opposite net geometry.
Not this one Both methods give Z-hex-3-ene
The dissolving-metal method has the complementary E preference.
Not this one Both methods necessarily give hexane
The specified partial-reduction conditions distinguish them from exhaustive hydrogenation.
Worked solution
An internal alkyne can become either alkene geometry depending on the reduction pathway. Since the substituents here are ethyl groups at both ends, same-side substituents are Z and opposite-side substituents are E.
What you'll practice
Compare net selectivity of two alkyne reduction methods.
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