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Answer: (i) C3H8: one structure (propane); (ii) C4H10: two structures (n-butane and isobutane); (iii) C3H4: propyne, propadiene (and cyclopropene).

(i) C3H8 — Propane (only one possible structure)

\(\text{CH}_3-\text{CH}_2-\text{CH}_3\)

(ii) C4H10 (two structural isomers)

1. n-Butane (straight chain): \(\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3\)

2. Isobutane (2-methylpropane, branched chain): \(\text{CH}_3-\underset{\displaystyle \text{CH}_3}{\underset{|}{\text{CH}}}-\text{CH}_3\)

(iii) C3H4

1. Propyne (triple bond): \(\text{CH}\equiv\text{C}-\text{CH}_3\)

2. Propadiene (two double bonds): \(\text{CH}_2=\text{C}=\text{CH}_2\)

3. Cyclopropene: a three-membered ring of carbon atoms with one C=C double bond (two CH groups joined by the double bond, and one CH2 group).

Check: each carbon has 4 bonds and each hydrogen 1 bond in every structure.

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Doubtly · 10 Oct 2021 Report
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Answer: C₃H₈ has 1 structure; C₄H₁₀ has 2 (butane and 2-methylpropane); C₃H₄ has 3 (propyne, propadiene and cyclopropene).

(i) \(\mathrm{C_3H_8}\): only one structure is possible.

  • Propane: \(\mathrm{CH_3{-}CH_2{-}CH_3}\)

(ii) \(\mathrm{C_4H_{10}}\): two structures (chain isomers).

  • n-Butane (butane): \(\mathrm{CH_3{-}CH_2{-}CH_2{-}CH_3}\) (straight chain)
  • Isobutane (2-methylpropane): \(\mathrm{CH_3{-}CH(CH_3){-}CH_3}\) (branched chain; the middle carbon carries a \(\mathrm{CH_3}\) group)

(iii) \(\mathrm{C_3H_4}\): this formula has two fewer pairs of H than propane, so it has a triple bond, two double bonds, or one double bond in a ring.

  • Propyne: \(\mathrm{CH{\equiv}C{-}CH_3}\) (one triple bond)
  • Propadiene: \(\mathrm{CH_2{=}C{=}CH_2}\) (two double bonds)
  • Cyclopropene: a three-carbon ring containing one C=C double bond, \(\mathrm{CH{=}CH}\) joined at both ends to a \(\mathrm{CH_2}\) group

When drawing the full structural formulae, show each carbon with four bonds and each hydrogen with one bond.

Doubtly AI · 23 Oct 2026 AI-verified · Oct 2026 Report
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