Alkyne Reactions and Synthesis Overview

Vocabulary practice flashcards covering alkyne structure, reduction methods, additions, oxidative cleavage, and synthesis reactions.

Alkyne

A hydrocarbon molecule containing two $\pi$ bonds (a triple bond) between carbon atoms, characterized by $sp$ hybridization and a linear geometry with a $180^\circ$ bond angle.

Lindlar's Catalyst

A poisoned metal catalyst used with $H_2$ to partially reduce an alkyne via syn addition to yield a cis-alkene.

Dissolving Metal Reduction

A reduction reaction using neutral sodium metal ($Na$) in liquid ammonia ($NH_3$) that proceeds through a radical intermediate to yield a trans-alkene.

Enol

An unstable intermediate containing an alcohol directly attached to an alkene carbon, which undergoes keto-enol tautomerization to isomerize into a carbonyl compound.

Acid-Catalyzed Hydration of Alkynes

A hydration reaction using $HgSO_4$, $H_2SO_4$, and $H_2O$ that adds an $OH$ to the more substituted carbon (Markovnikov addition) to form an enol, which tautomerizes into a ketone.

Hydroboration-Oxidation of Alkynes

A two-step reaction using a bulky boron reagent (such as $R_2BH$, Sia for disiamylborane, or 9-BBN) in THF followed by peroxide, base, and water to yield an anti-Markovnikov enol that tautomerizes into an aldehyde.

Geminal Dihalide

A compound with two halogen atoms bonded to the exact same carbon atom, typically formed when an alkyne reacts with excess $HX$.

Vicinal Dihalide

A compound containing two halogen atoms bonded to adjacent (neighboring) carbon atoms.

Halogenation of Alkynes

The addition of elemental halogen ($X_2$) across an alkyne; using excess reagent breaks both $\pi$ bonds to place two halogens on each carbon, adding a total of four halogens.

Ozonolysis of Internal Alkynes

An oxidative cleavage reaction using ozone ($O_3$) followed by $H_2O$ that cleaves both $\sigma$ and $\pi$ bonds of an internal alkyne to produce two carboxylic acids.

Ozonolysis of Terminal Alkynes

An oxidative cleavage reaction using $O_3$ followed by $H_2O$ that forms a carboxylic acid on the non-terminal end and carbon dioxide ($CO_2$) from the decomposition of formic acid at the terminal carbon.

Permanganate Oxidation under Weak/Neutral Conditions

Reaction of an alkyne with $KMnO_4$ under mild conditions that cleaves only the $\pi$ bonds without breaking the $\sigma$ bond, rearranging the intermediate polyols with water loss to produce a diketone.

Permanganate Oxidation under Hot Basic Conditions

An oxidative cleavage reaction using hot basic $KMnO_4$ that breaks both $\sigma$ and $\pi$ bonds to initially form carboxylate conjugate bases, which upon acidification with mild acid ($H_3O^+$) yield carboxylic acids.

Alkyne Synthesis via Double Elimination

A method to generate an alkyne from a geminal or vicinal dihalide by carrying out two elimination reactions using excess strong base, sodium amide ($NaNH_2$), in liquid ammonia.

Alkynide Anion (Acetylide Anion)

A carbon nucleophile formed when the acidic terminal hydrogen of an alkyne is deprotonated by a strong base like sodium amide ($NaNH_2$).

Alkyne Alkylation

A chain elongation synthetic reaction where an alkynide/acetylide anion acts as a nucleophile in an $S_N2$ attack on an alkyl carbon to displace a leaving group and create a longer carbon chain.