(a) (i) Draw the structures of the isomers of the alkene with molecular formurat C\(_4\)H\(_8\)
(ii) State the class of alkanols to which each of the following compounds belongs:
I. CH\(_3\)C(CH\(_3\))\(_2\)OH;
II. CH\(_3\)CH(CH\(_3\))CH\(_2\)OH;
III. CH\(_3\)CH\(_2\)CH(CH\(_3\))OH.
(b) (i) Write the formulae of the products formed in the following reactions:
I. CH\(_3\)CH\(_2\)COOH \(\frac{K_{(s)}}{}\)
II. CH\(_3\)CH\(_2\)COOH. \(\frac{C_4H_6OH, heat}{Conc.H_2SO_4}\)
III. CH\(_3\)CH\(_2\)CH\(_2\)CH\(_2\)OH \(\frac{H^+/KMnO_4}{(excess)}\)
(ii) Name the major product(s) of each of the reactions in (b)(i).
(c) A gaseous hydrocarbon R of mass 7.0 g occupies a volume of 2.24 dm\(^3\) at s. t.p. If the percentage composition by mass of hydrogen is 14.3, determine its:
(i) empirical formula;
(ii) molecular formula. [ H = 1.00, C = 12.0, Molar volume of gas at s.t.p, = 22.4 dm\(^3\) ]
(d) Define structural isomerism.
(a)(i) Isomers of the alkene \(C_4H_8\):
- But-1-ene: \(CH_2=CH-CH_2-CH_3\)
- But-2-ene: \(CH_3-CH=CH-CH_3\)
- 2-Methylpropene (methylpropene): \((CH_3)_2C=CH_2\)
(But-2-ene also shows cis and trans geometric forms.)
(ii) Class of alkanols:
- I. \(CH_3C(CH_3)_2OH\) (2-methylpropan-2-ol): tertiary alkanol.
- II. \(CH_3CH(CH_3)CH_2OH\) (2-methylpropan-1-ol): primary alkanol.
- III. \(CH_3CH_2CH(CH_3)OH\) (butan-2-ol): secondary alkanol.
(b)(i) Products:
- I. \(CH_3CH_2COOH\) with potassium metal, K: gives potassium propanoate and hydrogen, \[2CH_3CH_2COOH + 2K \rightarrow 2CH_3CH_2COOK + H_2\]
- II. \(CH_3CH_2COOH\) with ethanol and conc. \(H_2SO_4\), heat (esterification): \[CH_3CH_2COOH + C_2H_5OH \rightarrow CH_3CH_2COOC_2H_5 + H_2O\]
- III. \(CH_3CH_2CH_2CH_2OH\) (butan-1-ol) with excess acidified \(KMnO_4\) (oxidation): \[CH_3CH_2CH_2CH_2OH \xrightarrow{H^+/KMnO_4} CH_3CH_2CH_2COOH\]
(ii) Major products: I. potassium propanoate (\(CH_3CH_2COOK\)); II. ethyl propanoate (\(CH_3CH_2COOC_2H_5\)); III. butanoic acid (\(CH_3CH_2CH_2COOH\)).
(c) Hydrocarbon R: mass 7.0 g, volume 2.24 dm\(^3\) at s.t.p.
\[\text{moles of R} = \frac{2.24}{22.4} = 0.1\,mol\]
\[\text{molar mass} = \frac{7.0}{0.1} = 70\,g\,mol^{-1}\]
Percentage of H = 14.3, so percentage of C = 85.7.
(i) Empirical formula:
| C | H |
|---|
| Mole ratio | \(\frac{85.7}{12}=7.14\) | \(\frac{14.3}{1}=14.3\) |
| Divide by 7.14 | 1 | 2 |
Empirical formula = \(CH_2\).
(ii) Molecular formula: \((CH_2)_n = 70\), so \(14n = 70\), \(n = 5\). Molecular formula = \(C_5H_{10}\).
(d) Structural isomerism is the existence of two or more compounds that have the same molecular formula but different structural formulae (different arrangement of their atoms).
(a)(i) Isomers of the alkene \(C_4H_8\):
- But-1-ene: \(CH_2=CH-CH_2-CH_3\)
- But-2-ene: \(CH_3-CH=CH-CH_3\)
- 2-Methylpropene (methylpropene): \((CH_3)_2C=CH_2\)
(But-2-ene also shows cis and trans geometric forms.)
(ii) Class of alkanols:
- I. \(CH_3C(CH_3)_2OH\) (2-methylpropan-2-ol): tertiary alkanol.
- II. \(CH_3CH(CH_3)CH_2OH\) (2-methylpropan-1-ol): primary alkanol.
- III. \(CH_3CH_2CH(CH_3)OH\) (butan-2-ol): secondary alkanol.
(b)(i) Products:
- I. \(CH_3CH_2COOH\) with potassium metal, K: gives potassium propanoate and hydrogen, \[2CH_3CH_2COOH + 2K \rightarrow 2CH_3CH_2COOK + H_2\]
- II. \(CH_3CH_2COOH\) with ethanol and conc. \(H_2SO_4\), heat (esterification): \[CH_3CH_2COOH + C_2H_5OH \rightarrow CH_3CH_2COOC_2H_5 + H_2O\]
- III. \(CH_3CH_2CH_2CH_2OH\) (butan-1-ol) with excess acidified \(KMnO_4\) (oxidation): \[CH_3CH_2CH_2CH_2OH \xrightarrow{H^+/KMnO_4} CH_3CH_2CH_2COOH\]
(ii) Major products: I. potassium propanoate (\(CH_3CH_2COOK\)); II. ethyl propanoate (\(CH_3CH_2COOC_2H_5\)); III. butanoic acid (\(CH_3CH_2CH_2COOH\)).
(c) Hydrocarbon R: mass 7.0 g, volume 2.24 dm\(^3\) at s.t.p.
\[\text{moles of R} = \frac{2.24}{22.4} = 0.1\,mol\]
\[\text{molar mass} = \frac{7.0}{0.1} = 70\,g\,mol^{-1}\]
Percentage of H = 14.3, so percentage of C = 85.7.
(i) Empirical formula:
| C | H |
|---|
| Mole ratio | \(\frac{85.7}{12}=7.14\) | \(\frac{14.3}{1}=14.3\) |
| Divide by 7.14 | 1 | 2 |
Empirical formula = \(CH_2\).
(ii) Molecular formula: \((CH_2)_n = 70\), so \(14n = 70\), \(n = 5\). Molecular formula = \(C_5H_{10}\).
(d) Structural isomerism is the existence of two or more compounds that have the same molecular formula but different structural formulae (different arrangement of their atoms).
