Alkenes and Alkynes: Addition Reactions: every key term you need (+ practice quiz)
25 flashcard terms for Organic Chemistry I Topic 7, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
The characteristic reaction of a pi bond, in which the electron-rich double bond attacks an electrophile and a nucleophile then bonds to the resulting electron-poor carbon.
Markovnikov regiochemistry
In an ionic addition the electrophile bonds to the carbon bearing more hydrogens, so the positive charge and then the nucleophile end up at the more substituted carbon.
Anti-Markovnikov regiochemistry
The reversed orientation, placing the added nucleophilic fragment on the less substituted carbon. It signals either a radical chain or a concerted boron-based pathway.
Hydrohalogenation
Addition of hydrogen halide across a double bond. The proton adds first to give the more stable cation, and halide then captures it, so rearrangement is possible.
Acid catalyzed hydration
Water adds across an alkene with catalytic strong acid, giving the alcohol with the hydroxyl on the more substituted carbon. A cation intermediate means the skeleton can shift.
Oxymercuration and reduction
A two-stage sequence giving the same orientation as acid hydration but with no rearrangement, because a bridged mercury-containing intermediate prevents a free cation from forming.
Hydroboration and oxidation
Borane adds across the pi bond in one concerted step and peroxide then replaces boron with hydroxyl, delivering the alcohol to the less substituted carbon with both new groups on the same face.
Halonium ion
A three-membered bridged cation formed when a halogen adds to a pi bond. Because it blocks one face, the incoming nucleophile must attack from the opposite side.
Anti addition
Two new groups added to opposite faces of the former double bond. It is the signature of any bridged intermediate, including halonium and protonated epoxide chemistry.
Syn addition
Two new groups delivered to the same face of the former double bond, characteristic of concerted four-center transition states and of reactions occurring on a metal surface.
Halohydrin formation
Running a halogen addition in water traps the bridged ion with solvent, so halogen and hydroxyl end up on opposite faces and on adjacent carbons in a predictable orientation.
Catalytic hydrogenation
Hydrogen gas adds across a pi bond on a metal surface such as palladium on carbon. Both hydrogens are delivered to the same face, and the reaction is strongly exothermic.
Heat of hydrogenation
The energy released when a pi bond is reduced. Comparing values across isomers ranks alkene stability directly, since all of them converge on the same alkane.
Epoxidation
A peroxyacid transfers a single oxygen to a double bond in one step, forming a strained three-membered ether ring with the original alkene geometry preserved.
Anti dihydroxylation
Opening an epoxide with aqueous acid or base places the two hydroxyl groups on opposite faces of what was the double bond, giving the trans diol.
Syn dihydroxylation
Osmium tetroxide or cold dilute permanganate adds both oxygens to the same face through a cyclic intermediate, giving the cis diol after workup.
Ozonolysis
Ozone cleaves a double bond completely, and the subsequent workup decides the products: a mild reductive workup stops at aldehydes and ketones rather than acids.
Oxidative cleavage analysis
Working backward from cleavage products reveals where the original double bond was, since each carbonyl carbon in the products was once an alkene carbon.
Cyclopropanation
A one-carbon unit adds across a double bond in a single step to give a three-membered ring, preserving the relative arrangement of substituents present in the alkene.
Alkyne hydration
Adding water across a triple bond with acid and a mercury catalyst gives an unstable enol that immediately converts to the ketone with the carbonyl at the more substituted position.
Tautomerization
Rapid interconversion between an enol and its carbonyl form by proton transfer and pi bond shift. The carbonyl form is far more stable and dominates at equilibrium.
Hydroboration of a terminal alkyne
A bulky borane adds once with boron on the terminal carbon, and oxidation gives an enol that tautomerizes to the aldehyde rather than the ketone.
Lindlar catalyst
A poisoned palladium catalyst that stops alkyne reduction at the alkene stage and delivers both hydrogens to one face, giving the cis geometric isomer.
Dissolving metal reduction
Sodium in liquid ammonia reduces an internal alkyne through radical anion intermediates that adopt the less crowded arrangement, giving the trans alkene.
Acetylide alkylation
A deprotonated terminal alkyne displaces a leaving group from an unhindered primary carbon, forming a new carbon-carbon bond and lengthening the chain.