(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 follow...

(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:

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).