Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
(i) Molecular formula of benzene: C₆H₆
Structure of benzene: It is a cyclic compound with alternating single and double bonds between six carbon atoms, each bonded to one hydrogen atom.
```
H H
| |
H—C C—H
‖ |
H—C C—H
| |
C = C
H H
```
(Hexagonal ring with alternating single and double bonds)
(ii) In a benzene molecule (C₆H₆):
- Single bonds (C–C and C–H): 9 (3 C–C single bonds + 6 C–H bonds)
- Double bonds (C=C): 3
(iii) Unsaturated hydrocarbons containing one or more triple bonds between carbon atoms are called alkynes. Example: Ethyne (C₂H₂).
Source: Chapter 4, Section 4.2.2 – Chains, Branches and Rings
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Explanation
- For (i), always write the molecular formula first, then draw the hexagonal ring clearly showing alternating double bonds.
- For (ii), count carefully: 3 C=C (double) + 3 C–C (single) + 6 C–H (single) = 9 single + 3 double. Examiners specifically look for both types stated separately.
- For (iii), the definition must include "triple bond" — this is the key word that distinguishes alkynes from alkenes (double bond). The textbook definition is direct and should be quoted closely.