mechanisms

Question 1

SN1 Reaction (Substitution Nucleophilic Unimolecular)

Answer 1

• Reactants: Alkyl halide (R-X) + Nucleophile
• Products: Substituted compound (R-Nu) + Halide ion (X-)
• Conditions: Polar protic solvent (e.g., water, ethanol), weak nucleophile
• Mechanism: Two-step mechanism (formation of a carbocation, nucleophile attacks carbocation)
• Key Feature: Rate depends on the alkyl halide (1st order reaction)

Question 2

SN2 Reaction (Substitution Nucleophilic Bimolecular)

Answer 2

• Reactants: Alkyl halide (R-X) + Strong nucleophile
• Products: Substituted compound (R-Nu) + Halide ion (X-)
• Conditions: Polar aprotic solvent (e.g., acetone, DMSO)
• Mechanism: One-step mechanism (nucleophile attacks from the back, displacing the leaving group)
• Key Feature: Rate depends on both nucleophile and alkyl halide (2nd order reaction)

Question 3

E1 Reaction (Elimination Unimolecular)

Answer 3

• Reactants: Alkyl halide (R-X) + Base
• Products: Alkene + Halide ion (X-)
• Conditions: Polar protic solvent, weak base
• Mechanism: Two-step mechanism (formation of a carbocation, base removes a proton, forming double bond)
• Key Feature: Forms more substituted (stable) alkene (Zaitsev’s rule)

Question 4

E2 Reaction (Elimination Bimolecular)

Answer 4

• Reactants: Alkyl halide (R-X) + Strong base
• Products: Alkene + Halide ion (X-)
• Conditions: Strong base, polar aprotic solvent
• Mechanism: One-step mechanism (concerted loss of a proton and leaving group)
• Key Feature: Forms more substituted alkene (Zaitsev’s rule)

Question 5

Hydration of Alkenes

Answer 5

• Reactants: Alkene + Water (H2O)
• Products: Alcohol
• Conditions: Acid catalyst (H+), heat
• Mechanism: Electrophilic addition (protonation of alkene, nucleophilic attack by water, deprotonation to form alcohol)
• Key Feature: Follows Markovnikov’s rule (adds OH to more substituted carbon)

Question 6

Hydrohalogenation of Alkenes

Answer 6

• Reactants: Alkene + HX (HCl, HBr, etc.)
• Products: Alkyl halide (R-X)
• Conditions: No catalyst required, room temperature
• Mechanism: Electrophilic addition (protonation of alkene, halide attacks carbocation)
• Key Feature: Follows Markovnikov’s rule (X adds to more substituted carbon)

Question 7

Oxidation of Alcohols

Answer 7

• Reactants: Primary or Secondary Alcohol + Oxidizing agent (e.g., KMnO4, CrO3)
• Products: Primary alcohols → Aldehydes → Carboxylic acids; Secondary alcohols → Ketones
• Conditions: Acidic or basic medium
• Mechanism: Removal of H from OH group, formation of carbonyl group
• Key Feature: Tertiary alcohols do not oxidize

Question 8

Nitration of Benzene

Answer 8

• Reactants: Benzene + HNO3 (Nitric Acid)
• Products: Nitrobenzene + Water
• Conditions: Concentrated H2SO4 (sulfuric acid) as catalyst, heat
• Mechanism: Electrophilic aromatic substitution (formation of nitronium ion, attack on benzene, proton loss)
• Key Feature: Substitution at ortho/para positions if other groups are present

Question 9

Aldol Condensation

Answer 9

• Reactants: Aldehyde or Ketone with α-hydrogen + Base (e.g., NaOH)
• Products: β-hydroxyaldehyde or β-hydroxyketone (Aldol product), followed by dehydration to form an α,β-unsaturated aldehyde or ketone
• Conditions: Basic medium, heat
• Mechanism: Enolate formation, nucleophilic attack on carbonyl carbon, dehydration
• Key Feature: Forms a conjugated system after dehydration