Substitution, addition, elimination, and oxidation reactions

1. Substitution Reactions

1. Substitution reactions involve replacing one atom or group in a molecule with another.
2. Common in alkanes, alkyl halides, and aromatic compounds.
3. Types of substitution reactions:
   • SN1 reaction (Unimolecular nucleophilic substitution): Follows a two-step mechanism, rate depends on the concentration of the substrate.
   • SN2 reaction (Bimolecular nucleophilic substitution): Follows a single-step mechanism, rate depends on both the substrate and the nucleophile.
   • Electrophilic substitution: Common in aromatic compounds, such as nitration, halogenation, and sulfonation.
4. Example: CH₃-Cl + OH⁻ → CH₃-OH + Cl⁻ (nucleophilic substitution).

2. Addition Reactions

1. Addition reactions occur when two or more atoms or groups are added to a molecule, usually across a double or triple bond.
2. Common in alkenes and alkynes.
3. Types of addition reactions:
   • Electrophilic addition: Addition of an electrophile followed by a nucleophile (e.g., addition of HBr to ethene).
   • Nucleophilic addition: Common in carbonyl compounds (e.g., addition of HCN to aldehydes).
   • Free radical addition: Involves radicals, such as the addition of HBr in the presence of peroxides (anti-Markovnikov addition).
4. Example: C₂H₄ + H₂ → C₂H₆ (hydrogenation).

3. Elimination Reactions

1. Elimination reactions involve the removal of atoms or groups from adjacent carbon atoms, leading to the formation of a double or triple bond.
2. Common in alkyl halides and alcohols.
3. Types of elimination reactions:
   • E1 reaction (Unimolecular elimination): Follows a two-step mechanism; rate depends on the substrate.
   • E2 reaction (Bimolecular elimination): Follows a single-step mechanism; rate depends on both the substrate and the base.
   • Hofmann elimination: Leads to the formation of the least substituted alkene.
4. Example: CH₃-CH₂-Cl + KOH → CH₂=CH₂ + KCl + H₂O.

4. Oxidation Reactions

1. Oxidation reactions involve the increase in the oxidation state of carbon by adding oxygen or removing hydrogen.
2. Common in alcohols, aldehydes, and ketones.
3. Types of oxidation:
   • Alcohol oxidation:
     • Primary alcohols oxidize to aldehydes and further to carboxylic acids.
     • Secondary alcohols oxidize to ketones.
     • Tertiary alcohols resist oxidation.
   • Ozonolysis: Cleavage of alkenes or alkynes with ozone to form carbonyl compounds.
   • Combustion: Hydrocarbons burn in oxygen to produce CO₂ and H₂O.
4. Example: CH₃-CH₂-OH + [O] → CH₃CHO + H₂O (oxidation of ethanol to acetaldehyde).

5. Key Differences Between Reaction Types

1. Substitution: One group is replaced by another.
2. Addition: Groups are added to a molecule, typically across multiple bonds.
3. Elimination: Groups are removed, leading to the formation of multiple bonds.
4. Oxidation: Involves the addition of oxygen or removal of hydrogen.

6. Applications of These Reactions

1. Substitution: Used in the synthesis of halides, amines, and other functional groups.
2. Addition: Important in polymer production and hydrogenation processes.
3. Elimination: Key for the production of alkenes and alkynes.
4. Oxidation: Crucial for producing aldehydes, ketones, acids, and combustion processes.