(A) (i) Draw the structure of the following compounds :
(a) Butanoic acid
(b) Chloropentane
(ii) How are structure (i) and structure (ii) given below related to one another ? Give reason to justify your answer. Draw one more possible structure for above case.
(iii) Differentiate between saturated and unsaturated carbon compounds on the basis of their general formula.
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
(i) Structures:
(a) Butanoic acid (C₃H₇COOH):
$$\text{CH}_3 - \text{CH}_2 - \text{CH}_2 - \text{COOH}$$
(b) Chloropentane (C₅H₁₁Cl):
$$\text{CH}_3 - \text{CH}_2 - \text{CH}_2 - \text{CH}_2 - \text{CH}_2 - \text{Cl}$$
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(ii) Structures (i) and (ii) are related as structural isomers.
Reason: Both have the same molecular formula but different structural arrangements. Such compounds with identical molecular formula but different structures are called structural isomers.
One more possible structure (e.g., for C₄H₁₀):
$$\text{CH}_3 - \underset{|}{\overset{|}{\text{CH}}} (\text{CH}_3) - \text{CH}_3 \quad \text{(2-methylpropane)}$$
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(iii) Difference based on general formula:
| | Saturated | Unsaturated |
|---|---|---|
| General formula | CₙH₂ₙ₊₂ (alkanes) | CₙH₂ₙ (alkenes) / CₙH₂ₙ₋₂ (alkynes) |
| Bonds | Only single bonds | Double or triple bonds between C atoms |
Source: Chapter 4 — Carbon and its Compounds, Sections 4.2.1 and 4.2.2
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Explanation
- Structural isomers is the key term examiners look for in part (ii); always define it and give a reason.
- For part (iii), simply stating the general formula difference and linking it to single vs. double/triple bonds covers full marks. A small table makes it neat and saves words.
- In part (i), write structures as displayed/condensed formulae; electron dot structures are not needed unless specifically asked.
- Budget your time: parts (i) and (ii) together carry most marks; part (iii) needs only 2–3 lines.