Alcohols and Hydrogen Halides

• Alcohols: Organic molecules that include one or more hydroxyl (-OH) groups.
  • General Formula: R-OH, where R represents an alkyl group.
  • Common Examples:
    • Methanol: Utilised as fuel and a solvent.
    • Ethanol: Found in alcoholic beverages and hand sanitisers.

• Hydrogen Halides (HX): Chemical compounds composed of hydrogen and halogens.
  • Common Types: Include HCl, HBr, and HI.
  • Properties: Known for being strong acids and highly volatile.

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Substitution Reactions of Alcohols

Introduction to Substitution Reactions

• Substitution reactions involve the replacement of one group in a molecule:
  • In Alcohols: The hydroxyl group (-OH) is replaced by a halide ion (X$^-$).

SN1 and SN2 Mechanisms

SN1 Mechanism

• Unimolecular nucleophilic substitution:
  • Two-step process:
    1. Carbocation Formation: The leaving group exits, forming a carbocation.
    2. Nucleophilic Attack: The halide ion attacks the carbocation.
  • Typically occurs in tertiary alcohols.

SN2 Mechanism

• Bimolecular nucleophilic substitution:

  • One-step process:
    • The attack by the nucleophile and departure of the leaving group occur simultaneously.
  • Typically occurs in primary alcohols.

• Inversion of Configuration: Also referred to as Walden inversion.

Competing Mechanisms and Reaction Conditions

• Examples and Conditions:
  • The mechanisms compete based on the structure of the substrate, solvents, and type of halides.
• Transition States and Reaction Coordinate Diagrams:

Reaction Conditions

• Impact of Conditions: The conditions affect both the rate and the product of reactions:
  • Catalysts and temperature are primary influencing factors.

Differential Conditions

• Tertiary Alcohols: Often react readily without the need for catalysts.
• Secondary Alcohols: Typically require moderate conditions.
• Primary Alcohols: Generally necessitate catalysts such as zinc chloride.

Practical Examples and Applications

Reaction Equations

• Visualising changes:
  • Example Reaction: $\text{R-OH} + \text{HX} \rightarrow \text{R-X} + \text{H}_2\text{O}$

Carbocation Stability

• SN1: This pathway involves carbocations, favouring tertiary alcohols.
• SN2: This pathway involves a backside attack, favouring primary alcohols.

Safety Considerations

• Use of Personal Protective Equipment (PPE): Essential to safeguard against hazardous chemicals.
• Fume Hoods: Effective in venting harmful vapours.

• Chemical Handling: Involves appropriate storage and spill response measures.

Environmental Considerations

• Proper Disposal: Essential to prevent environmental harm.
• Sustainable Practices: Prioritise recycling and the use of less hazardous materials.