Chemical properties of organic compounds

1. Hydrocarbons

Hydrocarbons are divided into alkanes, alkenes, and alkynes, each with different properties and reactivities.

1.1 Alkanes $(CₙH₂ₙ₊₂)$

• Saturated hydrocarbons (only single bonds).
• Relatively unreactive due to strong $C-C$ and $C-H$ bonds.
• Low boiling points and evaporate easily.
• Used as fuels due to their ability to release energy when burned.
• Examples: Butane (lighter gas), petrol, paraffin.

1.2 Alkenes $(CₙH₂ₙ)$

• Unsaturated hydrocarbons (contain at least one double bond).
• More reactive than alkanes.
• Used in the manufacture of plastics (e.g. ethene for polyethene).
• Example: Ethene $(C₂H₄).$

1.3 Alkynes $(CₙH₂ₙ₋₂)$

• Highly unsaturated hydrocarbons (contain at least one triple bond).
• Very reactive.
• Used as industrial fuels and in welding (e.g. ethyne/acetylene burns at high temperatures).

2. Haloalkanes (Halogenated Alkanes)

• Alkanes with halogens (e.g. $Br, Cl, I$) attached.
• Saturated hydrocarbons, relatively unreactive.
• Poisonous and can be used as solvents, anaesthetics, or in dry cleaning.
• Example: Chloroform $(CHCl₃)$ used as an anaesthetic.

Environmental Impact

• Chlorofluorocarbons $(CFCs)$, once used in refrigerants and aerosols, contribute to ozone depletion and are being phased out.

3. Alcohols $(CₙH₂ₙ₊₁OH)$

• Saturated compounds with a hydroxyl $(-OH)$ functional group.
• Strong hydrogen bonding makes them soluble in water and have higher boiling points than hydrocarbons.
• Used in fuels, solvents, and alcoholic beverages.
• Examples:
  • Methanol $(CH₃OH) –$ toxic, used in methylated spirits.
  • Ethanol $(C₂H₅OH) –$ found in alcoholic drinks.

Types of Alcohols

1. Primary Alcohols – Hydroxyl $(-OH)$ attached to a carbon bonded to one other carbon. (e.g. propan-1-ol).
2. Secondary Alcohols – Hydroxyl $(-OH)$ attached to a carbon bonded to two other carbons. (e.g. propan-2-ol).
3. Tertiary Alcohols – Hydroxyl $(-OH)$ attached to a carbon bonded to three other carbons. (e.g. methylpropan-2-ol).

4. Aldehydes $(CₙH₂ₙO)$ & Ketones $(CₙH₂ₙO)$

• Contain a carbonyl group $(-C=O).$
• Aldehydes: Carbonyl group is on the first carbon (e.g. propanal).
• Ketones: Carbonyl group is on an inner carbon (e.g. propanone).
• Functional isomers of each other.
• Used in solvents, perfumes, and flavouring.

5. Carboxylic Acids $(CₙH₂ₙO₂)$

• Contain a carboxyl $(-COOH)$ functional group.
• Highly polar and can form hydrogen bonds → high boiling points.
• Weak acids, donate $H⁺$ in solution.
• Used in food preservatives and manufacturing.
• Examples:
  • Methanoic acid (formic acid) – found in insect stings.
  • Ethanoic acid (acetic acid) – found in vinegar.

6. Esters $(CₙH₂ₙO₂)$

• Functional isomers of carboxylic acids but have an $O-C=O$ functional group.
• Pleasant fruity odour.
• Used in perfumes, food flavouring, and plasticisers.
• Example: Ethyl ethanoate (used in nail polish remover).

Key Takeaways

• Alkanes = Saturated, unreactive, used as fuels.
• Alkenes & Alkynes = Unsaturated, reactive, used in plastics and welding.
• Haloalkanes = Contain halogens, used as solvents and refrigerants.
• Alcohols = Hydroxyl $(-OH)$ group, polar, used in fuels and beverages.
• Aldehydes & Ketones = Contain carbonyl $(-C=O)$ groups, used in solvents and perfumes.
• Carboxylic Acids = Weak acids, used in food preservatives and vinegar.
• Esters = Fruity-smelling, used in perfumes and flavouring.