Topic 1 · 11.1–11.2 · Free
Topic Notes · Easy summaries with diagrams
Chapter 11 — chapter 11
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📘Easy summary
Hydrocarbons contain only carbon and hydrogen. Aliphatic hydrocarbons are open-chain (or cyclic non-aromatic) compounds: alkanes (CₙH₂ₙ₊₂, single bonds, saturated), alkenes (CₙH₂ₙ, C=C) and alkynes (CₙH₂ₙ₋₂, C≡C). Aromatic hydrocarbons contain a benzene ring with delocalised π electrons (benzene, toluene). Alkanes (paraffins, 'little affinity') have sp³ carbon atoms, tetrahedral bond angles of 109.5°, and cycloalkanes (CₙH₂ₙ) are ring alkanes; cyclohexane exists in chair and boat forms. Boiling points of alkanes rise with chain length and fall with branching; they are non-polar and insoluble in water.
⭐Key points
- Alkane CₙH₂ₙ₊₂, sp³, 109.5°.
- Aromatic = benzene ring.
- Branching lowers b.p.
🔬Diagram
🌿Real-life example
n-pentane b.p. 36 °C, neopentane 9.5 °C — branching reduces surface contact.
💡Exam tip
- Learn the general formulae.
✅Quick check
1. Cycloalkanes have the formula:
2. Carbon in alkanes is:
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