Organic Chemistry mechanisms Flashcards
Free Radical Substitution
Reactants: Alkane + Halogen (Cl₂ or Br₂)
Conditions: UV light
Steps:
Initiation: Cl₂ → 2Cl* (homolytic fission)
Propagation:
Cl* + CH₄ → CH₃* + HCl
CH₃* + Cl₂ → CH₃Cl + Cl*
Termination:
Cl* + Cl* → Cl₂
CH₃* + Cl* → CH₃Cl
CH₃* + CH₃* → C₂H₆
Electrophilic Addition (Alkenes)
Reactants: Alkene + HBr / Br₂ / H₂O
Conditions: Room temperature
Steps:
Double bond attacks the electrophile (e.g., Br₂ or H⁺ from HBr), forming a carbocation.
Nucleophile (Br⁻ or H₂O) attacks the carbocation to form the product.
Nucleophilic Substitution (Halogenoalkanes)
Reactants: Halogenoalkane + OH⁻ / CN⁻ / NH₃
Conditions:
With OH⁻: Aqueous, warm
With CN⁻: Ethanolic, reflux
With NH₃: Excess ammonia, ethanolic
Steps:
Nucleophile (OH⁻, CN⁻, or NH₃) attacks the partially positive carbon in C-X bond.
Halogen (X⁻) is displaced, forming the substitution product.
Elimination (Halogenoalkanes)
Reactants: Halogenoalkane + OH⁻ (in ethanol)
Conditions: Ethanolic solution, heat
Steps:
OH⁻ acts as a base, removing an H⁺ from a β-carbon.
Double bond forms between α- and β-carbon, and the halide ion (X⁻) is lost.
Electrophilic Substitution (Benzene)
Reactants: Benzene + Electrophile (e.g., NO₂⁺, Br⁺, R⁺, or RC=O⁺)
Conditions:
Nitration: HNO₃ + H₂SO₄, 50°C
Halogenation: Br₂ + AlBr₃ (or FeBr₃)
Friedel-Crafts Alkylation: RCl + AlCl₃
Friedel-Crafts Acylation: RCOCl + AlCl₃
Steps:
Electrophile is generated (e.g., NO₂⁺ from HNO₃/H₂SO₄).
Benzene’s π electrons attack the electrophile, forming a carbocation intermediate.
The intermediate loses a proton (H⁺), restoring aromaticity.
Nucleophilic Addition (Aldehydes and Ketones)
Reactants: Carbonyl compound (Aldehyde or Ketone) + Nucleophile (e.g., HCN)
Steps:
Nucleophile (CN⁻ or H⁻) attacks the partially positive carbon in C=O bond.
A tetrahedral intermediate forms, which then captures a proton (H⁺) to form the product (hydroxynitrile).
Reduction of Carbonyl Compounds (Nucleophilic Addition)
Reactants: Aldehyde or Ketone + Reducing Agent (NaBH₄)
Conditions: Aqueous solution
Steps:
Hydride ion (H⁻) from NaBH₄ attacks the carbonyl carbon, breaking the C=O bond.
The resulting alkoxide ion is protonated to form the alcohol.
Dehydration of Alcohols (Elimination)
Reactants: Alcohol
Conditions: Heat with concentrated H₂SO₄ or H₃PO₄
Steps:
Protonation of the -OH group by the acid catalyst.
Water is eliminated, leaving a carbocation intermediate.
A proton (H⁺) is lost, forming an alkene.
Esterification (Condensation Reaction)
Reactants: Carboxylic Acid + Alcohol
Conditions: Concentrated H₂SO₄, heat under reflux
Steps:
The -OH from the carboxylic acid and the H from the alcohol combine to form water.
The ester bond (R-COOR’) forms between the acid and alcohol.
Acylation (Nucleophilic Addition-Elimination)
Reactants: Acyl Chloride + Nucleophile (e.g., H₂O, NH₃, RNH₂, ROH)
Steps:
Nucleophile attacks the carbonyl carbon in the acyl chloride.
The intermediate loses Cl⁻, then a proton is eliminated to form the product (carboxylic acid, amide, or ester).
Hydrolysis of Esters
Reactants: Ester + Water (or Base)
Conditions:
Acidic hydrolysis: Heat with dilute acid (reversible).
Alkaline hydrolysis: Heat with NaOH (irreversible, forms carboxylate salt).
Steps:
Acidic hydrolysis: Ester + H₂O ⇌ Carboxylic acid + Alcohol.
Alkaline hydrolysis: Ester + OH⁻ → Carboxylate ion + Alcohol.
Nucleophilic Substitution (Amides)
Reactants: Acyl Chloride + Ammonia/Amine
Steps:
Ammonia (or amine) acts as a nucleophile, attacking the carbonyl carbon in the acyl chloride.
The intermediate loses Cl⁻, forming an amide.
Formation of Polyesters (Condensation Reaction)
Reactants: Dicarboxylic Acid + Diol
Conditions: Heat
Steps:
OH from the acid and H from the diol combine to form water.
Ester bond forms between the monomers.
Formation of Polyamides (Condensation Reaction)
Reactants: Dicarboxylic Acid + Diamine
Conditions: Heat
Steps:
OH from the acid and H from the amine combine to form water.
Amide bond forms between the monomers.
