Alcohols Overview - OCR-A Revision

Introduction to Alcohols

• Alcohols have the functional group OH (hydroxyl group).
• Alcohols belong to the homologous series: CₙH₂ₙ₊₁OH.
• Types of alcohols:
  • Primary Alcohol: OH group attached to a carbon bonded to one other carbon (e.g., butan-1-ol).
  • Secondary Alcohol: OH group attached to a carbon bonded to two other carbons (e.g., butan-2-ol).
  • Tertiary Alcohol: OH group attached to a carbon bonded to three other carbons.

Solubility of Alcohols

• OH bond in alcohols is polar; delta negative on oxygen.
• Hydrogen bonding occurs between alcohols and water, aiding solubility.
• Short-chain alcohols (e.g., methanol, ethanol) are more soluble due to less non-polar hydrocarbon chain.
• Longer hydrocarbon chains result in decreased solubility.

Boiling Points and Volatility

• Alcohols have higher boiling points than similar mass alkanes due to hydrogen bonding.
• Less volatile than alkanes.

Formation of Haloalkanes

• Haloalkanes formed via substitution reactions.
• Alcohol reacts with halide ions and an acid catalyst (e.g., sodium bromide + sulfuric acid) to form haloalkane (e.g., 2-bromobutane).

Dehydration of Alcohols

• Alcohols dehydrate to form alkenes by removing water.
• Requires acid catalysts (e.g., sulfuric or phosphoric acid).
• Useful for creating polymers and plastics.
• Non-primary alcohols > 3 carbons can form different positional isomers and E/Z isomers.

Combustion of Alcohols

• Alcohols burn with a light blue flame, forming CO₂ and H₂O.
• Can be oxidized with potassium dichromate, forming aldehydes, ketones, or carboxylic acids.

Oxidation of Alcohols

• Primary Alcohols can be oxidized:
  • To Aldehydes, then further to Carboxylic Acids.
  • Requires distillation to capture aldehyde before further oxidation.
  • Reflux used for full oxidation to carboxylic acids, allowing strong heating without loss.
• Secondary Alcohols oxidized to Ketones only, using reflux.
• Primary can't oxidize further with potassium dichromate.

Practical Techniques

• Distillation: Used to isolate aldehydes by removing them as they form.
• Reflux: Allows strong heating without losing volatile compounds, used for full oxidation to carboxylic acids.

Conclusion

• Key reactions and properties of alcohols are covered, essential for OCR-A exams.
• Further support and resources are available for deeper study.