VerChem

SN2 Reaction

A one-step concerted mechanism where the nucleophile attacks the electrophilic carbon from the back side (180°) while the leaving group departs simultaneously. The reaction proceeds with inversion of configuration (Walden inversion) at the stereocenter.

SN1 Reaction

A two-step mechanism: the leaving group departs first to form a planar carbocation intermediate, then the nucleophile attacks. Since the carbocation is sp²-hybridized (planar), the nucleophile can attack from either face, leading to racemization.

E2 Elimination

A concerted one-step mechanism where the base abstracts a proton anti-periplanar to the leaving group. The C-H and C-LG bonds break simultaneously while the C=C double bond forms. Follows Zaitsev's rule: the more substituted alkene is the major product.

E1 Elimination

A two-step mechanism where the leaving group departs first to form a carbocation, followed by deprotonation of a β-hydrogen to form the alkene. Often occurs alongside SN1.

Markovnikov Addition

Electrophilic addition of hydrogen halides to alkenes following Markovnikov's rule: the hydrogen adds to the less substituted carbon (the one with more H's), and the halide adds to the more substituted carbon. This is because the more stable carbocation intermediate forms.

Anti-Markovnikov Addition

Morris Kharasch (1933)

Radical chain addition of HBr to alkenes. Peroxides generate radicals that reverse the normal Markovnikov selectivity. The bromine adds to the less substituted carbon because the more stable radical intermediate forms at the more substituted position.

Halogenation of Alkenes

Electrophilic addition of Br₂ or Cl₂ to alkenes proceeds through a cyclic halonium ion intermediate, giving exclusively anti addition (trans product). This is one of the classic tests for unsaturation — Br₂ decolorization.

Catalytic Hydrogenation

Both H atoms add to the same face of the double bond (syn addition) because the reaction occurs on the surface of the metal catalyst. The alkene adsorbs onto the catalyst surface, H₂ dissociates on the metal, and both hydrogens are delivered from the same face.

Acid-Catalyzed Hydration

Addition of water across a double bond following Markovnikov's rule. The OH group ends up on the more substituted carbon via carbocation intermediate. An alternative is oxymercuration-demercuration which avoids rearrangements.

Fischer Esterification

Emil Fischer (1895)

Acid-catalyzed condensation of a carboxylic acid with an alcohol to form an ester. The reaction is an equilibrium, so water removal (Dean-Stark trap) or excess alcohol drives it to completion.

Saponification

Irreversible base hydrolysis of an ester to give a carboxylate salt and an alcohol. The name comes from soap-making (saponification of fats). Unlike acid hydrolysis, this is irreversible because the carboxylate anion product is very stable.

Free Radical Halogenation

Substitution of a C-H bond by C-X through a radical chain mechanism. Bromination is highly selective for tertiary C-H bonds (1600:80:1 for 3°:2°:1°), while chlorination is less selective (5:4:1).

Alcohol Dehydration

Elimination of water from an alcohol to form an alkene. Tertiary alcohols are easiest (E1 mechanism), primary alcohols require higher temperatures (E2-like). Follows Zaitsev's rule: more substituted alkene is the major product.

Electrophilic Aromatic Substitution

The characteristic reaction of aromatic rings: an electrophile replaces a hydrogen on the ring while preserving aromaticity. The mechanism involves formation of a non-aromatic carbocation intermediate (arenium ion/sigma complex) followed by deprotonation to restore aromaticity.

Hydroboration-Oxidation

Herbert C. Brown (1959)

A two-step sequence: (1) Hydroboration — BH₃ adds across the alkene with syn stereochemistry and anti-Markovnikov regiochemistry (B goes to less substituted C). (2) Oxidation — H₂O₂/NaOH replaces B with OH with retention of configuration. Nobel Prize 1979.

Grignard Reaction

Victor Grignard (1900)

The Grignard reagent (RMgBr) is a powerful organometallic nucleophile that adds to carbonyl compounds. Formaldehyde → 1° alcohol, aldehydes → 2° alcohol, ketones → 3° alcohol, esters → 3° alcohol (two equivalents add). Nobel Prize 1912.

Aldol Condensation

Charles-Adolphe Wurtz (1872)

An enolate (or enol) of one carbonyl compound attacks the carbonyl of another. The aldol addition product is a β-hydroxy carbonyl compound. Heating causes dehydration to the α,β-unsaturated carbonyl (aldol condensation). This forms a new C-C bond.

Wittig Reaction

Georg Wittig (1954)

Converts a C=O to a C=C: the phosphorus ylide reacts with an aldehyde/ketone to give an alkene and triphenylphosphine oxide. The position of the new double bond is unambiguous (unlike elimination). Nobel Prize 1979.

Diels-Alder Reaction

Otto Diels, Kurt Alder (1928)

A concerted [4+2] pericyclic cycloaddition: a conjugated diene (4π) reacts with a dienophile (2π) to form a new 6-membered ring with one C=C. The diene must be in s-cis conformation. Suprafacial on both components. Nobel Prize 1950.

Claisen Condensation

Rainer Ludwig Claisen (1887)

The ester analog of the aldol reaction: an ester enolate attacks the carbonyl of another ester molecule, followed by loss of alkoxide to give a β-keto ester. Driven forward by deprotonation of the acidic α-H between the two carbonyls.

Michael Addition

Arthur Michael (1887)

Conjugate (1,4-) addition of a stabilized nucleophile (Michael donor) to an α,β-unsaturated carbonyl (Michael acceptor). The nucleophile adds to the β-carbon rather than the carbonyl carbon, giving a 1,5-dicarbonyl relationship.

Friedel-Crafts Alkylation

Charles Friedel, James Crafts (1877)

Lewis acid-catalyzed electrophilic aromatic substitution where an alkyl group is introduced onto the aromatic ring. AlCl₃ generates a carbocation (or carbocation-like) electrophile from the alkyl halide.

Friedel-Crafts Acylation

Charles Friedel, James Crafts (1877)

Lewis acid-catalyzed introduction of an acyl group (C=O-R) onto an aromatic ring. Superior to FC alkylation because: (1) no rearrangements (acylium ion is resonance-stabilized), (2) no polyacylation (product is deactivated), (3) can reduce C=O later for net alkylation.

Williamson Ether Synthesis

Alexander Williamson (1850)

SN2 reaction between an alkoxide nucleophile and a primary (or methyl) alkyl halide to form an ether. The key planning decision is which oxygen becomes the alkoxide and which carbon bears the halide — always make the less hindered partner the halide.

Jones Oxidation

A strong Cr(VI) oxidation that converts primary alcohols all the way to carboxylic acids and secondary alcohols to ketones. Cannot stop at the aldehyde stage for primary alcohols (use PCC or Swern for that).

PCC Oxidation

A mild, selective Cr(VI) oxidant that converts primary alcohols to aldehydes (without over-oxidation to carboxylic acid) and secondary alcohols to ketones. The anhydrous conditions (CH₂Cl₂) prevent the aldehyde hydrate from forming.

Swern Oxidation

Daniel Swern (1978)

A mild, chromium-free oxidation that converts alcohols to aldehydes/ketones. Uses activated DMSO as the oxidant. Must be performed at -78°C to avoid Pummerer rearrangement side products.

NaBH₄ Reduction

A mild reducing agent that selectively reduces aldehydes and ketones to alcohols without reducing esters, amides, or carboxylic acids. Delivers hydride (H⁻) to the electrophilic carbonyl carbon.

LiAlH₄ Reduction

A powerful, non-selective reducing agent that reduces virtually all C=O containing functional groups. Much stronger than NaBH₄. Must use anhydrous conditions (reacts violently with water). Reduces esters to two alcohols, acids to primary alcohols, amides to amines.

Wolff-Kishner Reduction

Nikolai Kishner, Ludwig Wolff (1911)

Complete removal of a C=O group, replacing it with CH₂. The ketone/aldehyde is first converted to a hydrazone, then heated with strong base to lose N₂ gas. Basic conditions — complementary to Clemmensen (acidic conditions).

Suzuki-Miyaura Coupling

Akira Suzuki (1979)

Palladium-catalyzed cross-coupling of an organoboron compound with an aryl halide. The most widely used cross-coupling reaction due to mild conditions, tolerance of many functional groups, and stability of boronic acids. Nobel Prize 2010.

Heck Reaction

Tsutomu Mizoroki, Richard Heck (1972)

Palladium-catalyzed coupling of an aryl halide with an alkene. Unlike Suzuki, the alkene partner is used directly (no organometallic needed). Produces substituted alkenes with high E-selectivity. Nobel Prize 2010.

Sonogashira Coupling

Kenkichi Sonogashira (1975)

Palladium/copper co-catalyzed coupling of a terminal alkyne with an aryl halide. The copper acetylide intermediate undergoes transmetalation with the palladium complex. Creates sp-sp² C-C bonds.

Olefin Metathesis

Robert Grubbs, Richard Schrock (1992)

Alkene bonds are broken and reformed — substituents on the double bonds are "scrambled." The key intermediate is a metallacyclobutane. Ring-closing metathesis (RCM) is especially powerful for making medium and large rings. Nobel Prize 2005.

Sharpless Asymmetric Epoxidation

K. Barry Sharpless (1980)

Enantioselective epoxidation of allylic alcohols using Ti(OiPr)₄, a tartrate ester ligand, and TBHP as oxidant. The mnemonic: draw the allylic alcohol with OH in the lower right — L-(+)-DIPT delivers oxygen from the top, D-(-)-DIPT from the bottom. Nobel Prize 2001.

Beckmann Rearrangement

Ernst Otto Beckmann (1886)

Rearrangement of a ketoxime to an amide (or lactam from cyclic ketoximes). The group anti to the hydroxyl migrates to nitrogen. Industrially important: cyclohexanone oxime → caprolactam (nylon-6 precursor).

Baeyer-Villiger Oxidation

Adolf von Baeyer, Victor Villiger (1899)

Oxidation of a ketone to an ester (or lactone) using a peracid. An oxygen atom is inserted between the carbonyl and the adjacent carbon. The migratory aptitude determines which group migrates: 3° > 2° > 1° > methyl (also aryl migrates well).

Robinson Annulation

Robert Robinson (1935)

A tandem Michael addition followed by intramolecular aldol condensation that constructs a new 6-membered ring fused to the existing ketone. This one-pot reaction creates one ring, two C-C bonds, and three stereocenters.

Mannich Reaction

Carl Mannich (1912)

A three-component reaction: an enolizable carbonyl compound, formaldehyde, and an amine combine to form a β-amino carbonyl compound (Mannich base). Proceeds through an iminium ion intermediate that acts as the electrophile.

Sandmeyer Reaction

Traugott Sandmeyer (1884)

Conversion of an aryldiazonium salt to an aryl halide (Cl, Br) or nitrile (CN) using copper(I) salts. The diazonium salt is first prepared by treating the arylamine with NaNO₂/HCl at 0°C. Essential for introducing substituents not easily placed by direct EAS.