Hydrocarbons
World C — Carbon Chemistry
33.A — CLASSIFICATION & ALIPHATICS
C
R33.01 What are Hydrocarbons?
- Organic compounds containing only Carbon and Hydrogen.
- The simplest class of organic molecules.
- Chief components of petroleum and natural gas.
C
C
C
R33.02 Alkanes (Saturated)
- Only single bonds between carbon atoms.
- General Formula: $C_nH_{2n+2}$.
- Methane, Ethane, Propane. Ends in -ane.
- Tetrahedral geometry ($sp^3$).
C
C
R33.03 Alkenes (Unsaturated)
- Contain at least one C=C double bond.
- General Formula: $C_nH_{2n}$.
- Ethene, Propene. Ends in -ene.
- Trigonal planar geometry ($sp^2$).
C
C
R33.04 Alkynes (Unsaturated)
- Contain at least one $C\equiv C$ triple bond.
- General Formula: $C_nH_{2n-2}$.
- Ethyne (Acetylene). Ends in -yne.
- Linear geometry ($sp$).
33.B — RINGS & ISOMERS
R33.05 Aromatic Hydrocarbons
- Contain a planar ring with delocalized $\pi$ electrons.
- Follow Hückel's rule ($4n+2$ $\pi$ electrons).
- Benzene ($C_6H_6$) is the parent compound. Highly stable.
R33.06 Cyclic Aliphatics
- Carbon atoms joined in a closed ring, but without aromatic resonance.
- Cycloalkanes ($C_n H_{2n}$) like Cyclopentane.
- Behave chemically like their straight-chain analogs.
R33.08 Structural Isomerism
- Same molecular formula, different connectivity.
- Chain Isomers: Straight vs branched (e.g., n-butane vs isobutane).
- Branched isomers have lower boiling points (less surface area).
SAT
UNSAT
R33.07 Bromine Water Test
- Test to distinguish saturated vs unsaturated.
- Unsaturated hydrocarbons (Alkenes/Alkynes) rapidly decolorize orange bromine water.
- Saturated (Alkanes) show no immediate reaction.
33.C — CHEMICAL REACTIONS
CO₂
H₂O
R33.09 Combustion
- Burning in oxygen yields $CO_2$, $H_2O$, heat, and light.
- Alkanes: Clean blue flame (complete combustion).
- Alkenes/Aromatics: Yellow, sooty flame (higher carbon %. incomplete).
CH₄
R33.10 Substitution
- Characteristic reaction of Alkanes.
- One atom is swapped for another.
- Requires energy (e.g., UV light to substitute H with Cl to form Chloromethane).
R33.11 Addition
- Characteristic of Unsaturated hydrocarbons.
- Pi bond breaks, new atoms attach to the carbons.
- Hydrogenation: Adding $H_2$ (using Ni/Pd catalyst) converts vegetable oils to solid fats.
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R33.12 Fossil Fuels & Distillation
- Petroleum is a complex mixture of hydrocarbons.
- Separated by boiling point via Fractional Distillation.
- Smaller chains (Gas) boil first, long chains (Asphalt) stay at bottom.