Organic Chemistry: Substitution, Elimination, and Addition Reactions

Comprehensive vocabulary flashcards reviewing substitution, elimination, carbocation rearrangements, and addition reactions of alkenes and alkynes.

$S_N2$ Reaction

A bimolecular nucleophilic substitution reaction in which both the nucleophile and the electrophile are involved in the rate-determining step, proceeding via backside attack with inversion of stereochemistry.

Backside Attack

The nucleophilic attack trajectory in an $S_N2$ reaction where the nucleophile approaches the electrophilic carbon from the side opposite to the leaving group, causing stereochemical inversion.

E2 Reaction

A bimolecular elimination reaction in which a base abstracts a proton while the leaving group departs in the rate-determining step to produce an alkene.

$S_N1$ Reaction

A unimolecular nucleophilic substitution reaction in which only the electrophile (compound with the leaving group) is involved in the rate-determining step, proceeding through a carbocation intermediate.

1,2-Hydride Shift

The most common carbocation rearrangement, in which a hydrogen atom adjacent to a carbocation migrates with its electrons to yield a more stable carbocation.

1,2-Methyl Shift

The least common carbocation rearrangement, in which an adjacent methyl group migrates to the carbocation center only if the shift yields a significantly more stable carbocation.

Ring Expansion

A carbocation rearrangement occurring in substituted small cycloalkanes where a ring bond shifts to an adjacent exocyclic carbocation to form a larger, less strained ring.

E1 Reaction

A unimolecular elimination reaction where only the electrophile is involved in the rate-determining step to yield an alkene, typically competing with $S_N1$ pathways and favored at higher temperatures.

Electrophilic Addition

A two-step reaction in which an electrophile such as $HCl$, $HBr$, or $HI$ adds across an alkene double bond via a carbocation intermediate to yield an alkyl halide.

Halogenation

A two-step addition reaction where $Cl_2$ or $Br_2$ adds across an alkene via a cyclic chloronium or bromonium intermediate without forming a free carbocation.

Halohydrin

A compound containing a halogen and a hydroxyl group on adjacent carbons, formed when an alkene undergoes halogenation in the presence of water acting as the nucleophile.

Acid-Catalyzed Hydration

An electrophilic addition reaction in which water adds across an alkene in the presence of a strong acid catalyst to form an alcohol through a carbocation intermediate.

Epoxide

A three-membered cyclic ether compound that acts as a strong electrophile due to significant ring strain associated with its cyclopropyl geometry.

anti-Diol

A 1,2-diol product formed by acid-catalyzed opening of an epoxide with water, where the nucleophilic water molecule attacks from the back, adding anti to the preexisting hydroxyl group.

Tautomerization

A spontaneous equilibrium reaction that interconverts a vinyl alcohol (enol) and its more stable carbonyl isomer, which can be catalyzed by either acid or base.

Acetylide Anion

A carbanion formed by deprotonating the acidic terminal $C_{sp}-H$ bond ($pK_a = 24$) of an alkyne with a strong base such as $NH_2^-$ ($pK_a = 38$), useful as a nucleophile in substitution reactions.