Home / AS & A Level Chemistry 19.2 Nitriles and hydroxynitriles Exam Style Practice Questions Paper 1
Butanone, \(\mathrm{CH_3CH_2COCH_3}\), and \(\mathrm{HCN}\) mixed with a little \(\mathrm{KCN}\) react together in a nucleophilic addition reaction.
Which description of the mechanism of this nucleophilic addition reaction is correct?
Correct Answer: \( \boxed{\mathrm{D}} \)
The cyanide ion acts as the nucleophile using its lone pair to attack the \(\delta^+\) carbon atom of the carbonyl group.
This forms an alkoxide ion, which is then protonated when the oxygen atom accepts \(\mathrm{H^+}\) from \(\mathrm{HCN}\), producing the hydroxynitrile.
Therefore, the correct answer is (D).
Butylamine can be produced by the reaction of butanenitrile with hydrogen in the presence of a suitable catalyst.
Which volume of hydrogen, measured at room conditions, is required to react completely with \(0.500\,\mathrm{g}\) of butanenitrile?
Correct Answer: \( \boxed{\mathrm{D}} \)
Reduction of a nitrile requires two moles of hydrogen:
\(\mathrm{R{-}CN+2H_2\rightarrow R{-}CH_2NH_2}\)
Molar mass of butanenitrile:
\(\mathrm{C_4H_7N}=4(12)+7(1)+14=69\,\mathrm{g\,mol^{-1}}\)
Moles of butanenitrile:
\(\mathrm{\dfrac{0.500}{69}=7.25\times10^{-3}\,mol}\)
Moles of hydrogen required:
\(\mathrm{2\times7.25\times10^{-3}=1.45\times10^{-2}\,mol}\)
At room conditions, \(1\,\mathrm{mol}\) of gas occupies \(24000\,\mathrm{cm^3}\).
Volume of hydrogen:
\(\mathrm{1.45\times10^{-2}\times24000=348\,\mathrm{cm^3}}\)
Therefore, the correct answer is (D).
Which reaction mixture produces a nitrile?
Correct Answer: \( \boxed{\mathrm{A}} \)
Ethanolic potassium cyanide reacts with halogenoalkanes by nucleophilic substitution:
\(\mathrm{R{-}X+KCN\rightarrow R{-}CN+KX}\)
The product contains the nitrile functional group, \(\mathrm{-C\equiv N}\).
The other reactions produce amines, hydrazones or ammonium salts rather than nitriles.
Therefore, the correct answer is (A).