ORGANIC CHEMICAL CLASSIFICATION AND NOMENCLATURE
Introduction:
Organic chemistry is the study of carbon-containing compounds. Earlier, these compounds were obtained from living sources, but now they include all carbon-based compounds.
Carbon shows catenation, allowing formation of long chains and rings. Organic compounds may also contain hydrogen, oxygen, nitrogen, sulphur, halogens, and phosphorus.
Key concepts include structure, functional groups, homology, and isomerism.
Classification of Organic Compounds:
Organic compounds are classified based on structure and functional groups.
Structural Classification:
Based on carbon skeleton, compounds are classified into open-chain and closed-chain types.
Acyclic (Open-Chain) Compounds:
- Saturated compounds: Only single bonds (e.g., methane)
- Unsaturated compounds: Double or triple bonds (alkenes, alkynes)
Cyclic (Closed-Chain) Compounds:
These compounds form ring structures.
Types:
- Homocyclic compounds: Rings contain only carbon atoms
- Alicyclic (e.g., cyclohexane)
- Aromatic (e.g., benzene, naphthalene)
- Heterocyclic compounds: Rings contain heteroatoms (O, N, S)
- Alicyclic heterocycles (e.g., oxirane)
- Aromatic heterocycles (e.g., pyrrole, furan, thiophene)
Functional Groups:
Functional groups determine chemical properties and reactivity of compounds.
- –OH (Alcohol)
- –CHO (Aldehyde)
- –COOH (Carboxylic acid)
Compounds with same functional group show similar chemical behaviour.
Nomenclature of Organic Compounds:
Naming is required because many compounds may have the same formula but different structures.
- Trivial (common) system
- IUPAC system
Trivial Naming System:
- Based on source, property, discoverer, or structure
- Example: Formic acid (from ants)
- Not systematic and may create confusion
Limitations: Non-scientific, multiple names possible, not suitable for large number of compounds.
IUPAC Naming System:
IUPAC provides systematic naming rules.
General format: Prefix + Word root + Primary suffix + Secondary suffix
- Word root: Number of carbon atoms
- Primary suffix: Type of bond (–ane, –ene, –yne)
- Secondary suffix: Functional group (–ol, –al, –oic acid)
- Prefix: Substituents
Heterocyclic Compounds:
Contain rings with at least one heteroatom such as oxygen, nitrogen, or sulphur.
Naming Rules:
- O → oxa, N → aza, S → thia
- Ring size defines suffix
- Priority order: O > S > N
Examples: Oxirane, Thiophene, Pyridine
Fused Heterocyclic Rings:
- Formed when two rings share atoms
- Named using letter positions like [a], [b], [c]
- Examples: Benzo[b]furan, Benzo[c]thiophene
