Organic chemistry 2 slides review

Elimination reaction

Single reactant splits into two products.

Substitution reaction

Two reactants exchange parts to form two new products.

Addition reaction

Two reactants combine to form one product.

Rearrangement reaction

Single reactant becomes an isomer through reorganization of bonds.

Reaction mechanism

Step-by-step description of how reactants become products.

Homolytic cleavage

Symmetrical bond breaking; each atom gets one electron.

Heterolytic cleavage

Unsymmetrical bond breaking; one atom gets both electrons.

Radical

Neutral species with one unpaired electron; highly reactive.

Initiation step (radicals)

Radicals are first formed.

Propagation step (radicals)

Radicals react with molecules to make new radicals.

Termination step (radicals)

Two radicals combine to form a stable molecule.

Polar reaction

Reaction between nucleophile (electron-rich) and electrophile (electron-poor).

Nucleophile

Electron-pair donor; Lewis base.

Electrophile

Electron-pair acceptor; Lewis acid.

Carbocation

Positively charged carbon with only 6 valence electrons; sp² hybridized.

Curved arrow rule

Arrows show electron movement: always start at an electron source

Activation energy (Ea)

Minimum energy required for reaction to occur.

Transition state

Highest-energy point; bonds partially formed/broken.

Intermediate

Real species formed between steps; at an energy minimum.

Alkene

Hydrocarbon containing a C=C double bond; unsaturated.

Degree of unsaturation (DoU) formula

(2C + 2 − H) / 2

Cis isomer

Substituents on same side of double bond.

Trans isomer

Substituents on opposite sides of double bond.

E isomer

Higher priority groups on opposite sides.

Z isomer

Higher priority groups on the same side.

Hyperconjugation

Donation of electrons from σ bonds to empty p orbitals; stabilizes carbocations & alkenes.

Alkene stability trend

Tetrasubstituted > trisubstituted > disubstituted > monosubstituted.

Electrophilic addition

π bond attacks electrophile → carbocation → nucleophile attack.

Markovnikov’s Rule

H adds to carbon with more H’s (“rich gets richer”).

Regiospecific reaction

Only one orientation of addition occurs.

Carbocation stability trend

3° > 2° > 1° > methyl.

Inductive effect

Electron donation through σ bonds to stabilize carbocations.

Hammond postulate

Transition state resembles species (reactants or products) closest in energy.

Hydride shift

H with its electron pair moves to form a more stable carbocation.

Methyl shift

Alkyl group moves with electrons to stabilize carbocation.

Dehydrohalogenation

Elimination of HX from alkyl halide to form an alkene.

Dehydration

Elimination of water from alcohol to form alkene.

Halogenation (Br₂/Cl₂)

Addition of X₂ to alkene → 1

Bromonium ion

Three-membered ring intermediate formed during halogenation.

Anti addition

Atoms add to opposite sides of double bond.

Halohydrin formation (HOX)

Halogen + OH added across double bond; OH goes to more substituted carbon.

NBS

Safe source of Br⁺ for halohydrin formation.

Hydration (acid-catalyzed)

H₂O + H⁺ adds Markovnikov; carbocation rearrangements common.

Oxymercuration–demercuration

Markovnikov hydration without rearrangements; uses Hg²⁺ then NaBH₄.

Hydroboration-oxidation

Anti-Markovnikov addition of H and OH; syn addition; no rearrangements.

Syn addition

Both groups add to same face of double bond.

Catalytic hydrogenation

H₂ + metal catalyst → syn reduction of alkene to alkane.

Epoxidation (mCPBA)

Peroxyacid adds O to alkene → epoxide (same stereochemistry as alkene).

Anti-dihydroxylation

Epoxide + acid → trans-diol.

OsO₄ hydroxylation

Syn-diol formation.

Ozonolysis

Cleavage of C=C into carbonyls using O₃ + reductive workup.

KMnO₄ oxidation

Cleavage to acids or ketones; more aggressive than ozone.

Carbene addition

Carbene adds to alkene → cyclopropane.

Simmons–Smith reaction

CH₂I₂ + ZnCu → carbenoid; preserves alkene stereochemistry.