Organic Chemistry: Mechanisms and Reactions

Flashcards covering SN1/SN2/E1/E2 mechanisms, alkene/alkyne addition reactions, and radical chemistry based on the lecture transcript.

SN2 Mechanism

A 1-step, 2nd order nucleophilic substitution characterized by backside attack, inversion of stereochemistry, and the use of a strong nucleophile in polar aprotic solvents.

SN1 Mechanism

A 1st order nucleophilic substitution that occurs via a stable carbocation intermediate (tertiary, allylic, or benzylic), resulting in racemization using a weak nucleophile in polar protic solvents.

E2 Mechanism

A 2nd order beta-elimination that requires an anti-periplanar conformation between the proton and leaving group, typically using a strong base.

E1 Mechanism

A 1st order elimination reaction where the leaving group departs first to form a carbocation intermediate, usually favoring the Zaitsev product as the major product.

Anti-periplanar

The specific coplanar conformation required for E2 reactions where the hydrogen being removed and the leaving group are on opposite sides of the molecule.

Zaitsev Product

The more substituted alkene formed in an elimination reaction, which is typically the major product when using a small base.

Hofmann Product

The less substituted alkene formed in an elimination reaction, which becomes the major product when a bulky base is used.

Hydrohalogenation

The addition of HX across an alkene following Markovnikov's rule, involving a carbocation intermediate that may undergo rearrangement.

Acid-Catalyzed Hydration

The addition of water across an alkene using $H_2SO_4$ and $H_2O$ to form an alcohol following Markovnikov's rule, subject to carbocation rearrangements.

Oxymercuration-Demercuration

A two-step process using $Hg(OAc)_2, H_2O$ followed by $NaBH_4$ to achieve Markovnikov addition of alcohol without carbocation rearrangement.

Hydroboration-Oxidation (Alkenes)

A reaction using $BH_3 \times THF$ followed by $H_2O_2, NaOH$ to achieve anti-Markovnikov addition of an OH group via syn addition.

Catalytic Hydrogenation

The reduction of an alkene to an alkane using $H_2$ and a metal catalyst (like $Pt$), proceeding via syn addition.

Halogenation

The addition of $X_2$ (like $Cl_2$ or $Br_2$) across an alkene via anti addition, proceeding through a cyclic halonium ion intermediate.

Halohydrin Formation

The addition of $X_2$ and $H_2O$ across an alkene via anti addition, where the OH group adds to the more substituted position and the halogen adds to the less substituted position.

Anti Dihydroxylation

A reaction sequence using a peroxyacid like $RCO_3H$ (MCPBA) followed by acid-catalyzed ring opening with $H_3O^+$ to add two OH groups in an anti fashion.

Syn Dihydroxylation

The addition of two OH groups to the same side of an alkene using reagents like $OsO_4$ or cold, basic $KMnO_4$.

Ozonolysis (Alkenes)

The oxidative cleavage of an alkene using $O_3$ followed by a reducing agent like $DMS$ or $Zn/H_2O$ to form ketones or aldehydes.

Lindlar's Catalyst

A poisoned metal catalyst used to reduce an alkyne to a cis-alkene (syn addition).

Dissolving Metal Reduction

A reaction using $Na/NH_3 (l)$ to reduce an internal alkyne to a trans-alkene.

Hydration of Alkynes ($HgSO_4/H_2SO_4$)

An acid-catalyzed hydration of terminal alkynes that yields a methyl ketone via Markovnikov addition.

Hydroboration-Oxidation (Alkynes)

The use of a hindered borane (like $R_2BH$) followed by $H_2O_2, NaOH$ on a terminal alkyne to produce an aldehyde via anti-Markovnikov addition.

Initiation

The first step in a radical mechanism where heat or light ($hv$) causes the homolytic cleavage of a bond to create radicals.

Propagation

The repeating steps in a radical reaction where a radical reacts with a stable molecule to produce a new radical and a new stable product.

Termination

The final stage of a radical chain reaction where two radicals collide and form a covalent bond, eliminating the radical species.

Allylic Bromination

The use of $NBS/hv$ to selectively add a bromine atom to the allylic position, proceeding through a resonance-stabilized allylic radical.

Alkylation of Terminal Alkynes

A reaction involving the deprotonation of a terminal alkyne with a strong base ($NaNH_2$) to form an acetylide ion, which then performs an SN2 reaction on a methyl or primary alkyl halide.