ULTIMATE GUIDE TO CHEMICAL REACTIONS IN ORGANIC CHEMISTRY (ALKYNES):
Reaction Reaction Reaction Reagents Used Products
Intermediates Mechanism Formed
Deprotonation Acetylide anion Strong base Strong base Acetylide anion
(Acetylide removes acidic (e.g., NaNH₂) and conjugate
Formation) proton f rom acid of base
alkyne
SN² with Alkyl Transition state Nucleophilic Alkyl halide and Alkene
Halides substitution of acetylide anion
alkyl halide by
acetylide anion
Partial Alkene Catalytic H₂, Lindlar's Cis-alkene
Reduction hydrogenation catalyst
(Lindlar's with poisoned (Pd/CaCO₃,
Catalyst) catalyst Pb(OAc)₂)
Partial Radical anion Reduction with Na, NH₃ Trans-alkene
Reduction sodium metal in
(Na/NH₃) liquid ammonia
Hydroboration Vinylborane Anti- BH₃/THF, H₂O₂, Enol, which
Markovnikov NaOH tautomerizes to
addition of boron aldehyde/ketone
and hydrogen
Oxymercuration Mercurinium ion Markovnikov Hg(OAc)₂, H₂O, Enol, which
addition of NaBH₄ tautomerizes to
mercury and ketone
water
Addition of HX Vinyl halide Electrophilic HX (HCl, HBr, Vinyl halide
(Once) addition of HX to HI)
alkyne
Addition of HX Gem-dihalide Electrophilic Excess HX Gem-dihalide
(Twice) addition of HX to
vinyl halide
Hydrogenation Alkane Catalytic H₂, metal Alkane
hydrogenation catalyst (Pd/C,
with metal Pt/C)
catalyst
Ozonolysis Ozonide Oxidative O₃, H₂O₂ Carboxylic acids
cleavage of or ketones
alkyne
Oxidative Carboxylic acids Oxidative KMnO₄, H₂O Carboxylic acids
Cleavage cleavage of
(KMnO₄) alkyne with
strong oxidizing
agent
Halogenation Dihaloalkene or Electrophilic X₂ (Cl₂, Br₂, I₂) Dihaloalkene or
tetrahaloalkane addition of tetrahaloalkane
halogen to
alkyne
Alkyne Alkene Elimination of Strong base Alkyne
Formation via HX f rom (e.g., NaNH₂)
Elimination dihaloalkene
Notes:
• Acetylide anions are strong nucleophiles that can react with alkyl halides in SN²
reactions.
• Lindlar's catalyst is a poisoned catalyst that prevents over-reduction of the alkyne
to an alkane.
• Hydroboration and oxymercuration are regioselective reactions that follow anti-
Markovnikov and Markovnikov addition, respectively.
• Ozonolysis and oxidative cleavage are methods for cleaving alkynes into smaller
carbonyl compounds.
