JAMB Chemistry Note- Introduction to Organic Compounds

Definition of Organic Compounds

Organic compounds are chemical substances primarily composed of carbon and hydrogen, often combined with other elements like oxygen, nitrogen, sulfur, and halogens. These compounds are abundant in nature and form the basis of life, making up the structure of plants, animals, and other organisms. They are also the foundation for synthetic materials, fuels, and pharmaceuticals.

Tetravalency of Carbon

Tetravalency refers to the ability of carbon to form four covalent bonds with other atoms, including itself. This property arises from carbon’s electronic configuration: 1s² 2s² 2p², where it requires four electrons to complete its octet.

This property allows carbon to form stable structures such as:

• Straight chains (e.g., propane: CH₃-CH₂-CH₃)
• Branched chains (e.g., isobutane: CH₃-CH(CH₃)-CH₃)
• Rings (e.g., cyclohexane: C₆H₁₂)

Key Point: The ability of carbon to form long chains and rings is called catenation, and this is a unique characteristic of carbon among the elements.

Functional Groups

A functional group is a specific group of atoms within a molecule that determines the chemical properties of that compound. For example:

• Hydroxyl group (-OH): Found in alcohols (e.g., ethanol).
• Carboxyl group (-COOH): Found in acids (e.g., ethanoic acid).
• Carbonyl group (C=O): Found in aldehydes and ketones.

Classification of Organic Compounds by Functional Groups:

• Hydrocarbons: Contain only carbon and hydrogen.
• Alkanes: Saturated hydrocarbons (C-C single bonds).
• Alkenes: Unsaturated hydrocarbons (C=C double bonds).
• Alkynes: Unsaturated hydrocarbons (C≡C triple bonds).
• Aromatic hydrocarbons: Contain benzene-like rings.
• Alcohols (Alkanols): Contain the hydroxyl group (-OH).
• Aldehydes (Alkanals) and Ketones (Alkanones): Contain the carbonyl group (C=O).
• Carboxylic Acids (Alkanoic Acids): Contain the carboxyl group (-COOH).
• Esters (Alkanoates): Derived from carboxylic acids and alcohols.
• Amines: Contain nitrogen atoms (-NH₂, -NHR, -NR₂).

Empirical and Molecular Formula

Empirical Formula: The simplest ratio of atoms in a compound.
Example: The empirical formula of glucose (C₆H₁₂O₆) is CH₂O.

Molecular Formula: The actual number of atoms of each element in a compound.
Example: The molecular formula of glucose is C₆H₁₂O₆.

Steps to Determine Empirical Formula:

1. Obtain mass percentages of each element in the compound.
2. Convert percentages to moles by dividing by the atomic masses.
3. Divide by the smallest number of moles to get the simplest ratio.
4. Multiply by whole numbers, if necessary, to remove fractions.
5. Incorporate the valency of each element to cross-check the compound’s formula.

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Importance of Organic Chemistry

1. Biological Significance: Organic compounds like carbohydrates, proteins, and lipids are the building blocks of life.
2. Industrial Applications: Used in the manufacture of plastics, synthetic fibers, dyes, and pharmaceuticals.
3. Energy Sources: Hydrocarbons like methane, propane, and gasoline are essential fuels.
4. Agriculture: Fertilizers, pesticides, and herbicides are organic compounds.