Let’s break it down:
1. Aliphatic Compounds
- Definition: Organic compounds in which carbon atoms are arranged in open chains (straight or branched) or in non-aromatic rings.
- Types:
- Alkanes (saturated): Only single bonds (e.g., propane, C₃H₈).
- Alkenes (unsaturated): At least one double bond (e.g., ethene, C₂H₄).
- Alkynes (unsaturated): At least one triple bond (e.g., ethyne, C₂H₂).
- Alicyclic compounds: Non-aromatic rings (e.g., cyclohexane).
- Properties:
- Generally less stable than aromatic compounds.
- Do not follow special rules of aromaticity.
- Show addition or substitution reactions depending on saturation.
2. Aromatic Compounds
- Definition: Organic compounds containing at least one benzene ring or other aromatic ring system that satisfies Hückel’s rule (4n + 2 π electrons, where n = 0, 1, 2…).
- Examples: Benzene (C₆H₆), Toluene (C₆H₅CH₃), Naphthalene (C₁₀H₈).
- Properties:
- Highly stable due to resonance (delocalization of π electrons).
- Undergo substitution reactions rather than addition (to preserve aromaticity).
- Often have distinct odors (hence “aromatic”).
Key Differences at a Glance
Feature Aliphatic CompoundsAromatic Compounds Structure Open chains or non-aromatic rings Contain benzene ring or similar Electron system No delocalized π electrons Delocalized π electron cloud Stability Less stable Highly stable (resonance) Typical reactions Addition (for unsaturated), substitution Electrophilic substitution Examples Propane, Butene, Cyclohexane Benzene, Toluene, Phenol
In short: Aliphatic compounds are chain-like or non-aromatic, while aromatic compounds contain benzene-like rings with delocalized electrons.