Alkynes: An Introduction to Organic Synthesis

This set of vocabulary flashcards covers the fundamental concepts, electronic structures, chemical preparations, and reaction mechanisms of alkynes as presented in the organic chemistry lecture notes.

Alkynes

Hydrocarbons that contain carbon-carbon triple bonds.

Acetylene

The simplest alkyne, produced industrially from methane and steam at high temperature.

Organic synthesis

The preparation of organic molecules from simpler organic molecules.

Bond Energy (Acetylene)

The energy required to break a $\pi$ bond in acetylene ($HCCH$), which is $202\,kJ/mole$, compared to $269\,kJ/mole$ in ethylene.

Electronic Structure (Triple Bond)

Consists of one $\sigma$ bond formed by sp orbitals and two $\pi$ bonds formed by unhybridized $p_x$ and $p_y$ orbitals.

Vinyl halide

The intermediate produced during the two-fold elimination of $HX$ from a 1,2-dihaloalkane to form an alkyne.

Vicinal dihalides

Compounds available from the addition of bromine or chlorine to an alkene, used as precursors in alkyne preparation.

Markovnikov orientation

The regioselectivity rule followed by addition reactions of alkynes, such as the addition of $HX$ or mercury(II)-catalyzed hydration.

Vinylic carbocation

An intermediate in the addition of $HX$ to an alkyne; secondary versions form less readily than primary alkyl carbocations, while primary versions probably do not form at all.

Enol

A vinylic alcohol produced as the immediate product of mercury(II)-catalyzed hydration, which spontaneously transforms into a ketone or aldehyde.

Tautomers

Isomeric compounds that can rapidly interconvert by the movement of a proton.

Terminal alkyne

An alkyne where the triple bond is located at the first carbon of the chain.

Lindlar catalyst

A chemically deactivated palladium on calcium carbonate catalyst that converts alkynes into cis-alkenes via syn addition.

Radical anion

The intermediate involved in the reduction of alkynes to trans-alkenes using lithium or sodium in liquid ammonia.

Hydroboration-oxidation (Alkynes)

A process using borane followed by $H_2O_2$ that converts alkynes to ketones or aldehydes with anti-Markovnikov orientation.

Oxidative cleavage

A reaction using $O_3$ or $KMnO_4$ that breaks internal alkynes into two carboxylic acids and terminal alkynes into a carboxylic acid and $CO_2$.

Acetylide ion

An anion formed by the reaction of a strong anhydrous base with a terminal alkyne, which has a $pK_a$ of approximately $25$.

Alkylation

The reaction of acetylide ions with primary alkyl halides to produce a larger alkyne by forming a new carbon-carbon bond.

Dehydrohalogenation

A side reaction occurring when acetylide ions react with secondary or tertiary alkyl halides, converting the alkyl halide into an alkene instead of an alkyne.