Determining structures from analytical dataEdexcel International A Level Chemistry: Subtopic test

1. 1
   Compound X contains only carbon, hydrogen and oxygen. Combustion analysis shows that it contains 54.5% carbon and 9.1% hydrogen by mass. The mass spectrum of X has its molecular ion peak at m/z 88.

   (a)

   What is the empirical formula of X?

   [1 mark]

   • AC₂H₄O
   • BC₄H₈O₂
   • CCH₂O
   • DC₂H₆O

   (b)

   What is the molecular formula of X?

   [1 mark]

   • AC₂H₄O
   • BC₃H₄O₃
   • CC₄H₈O₂
   • DC₅H₁₂O

   (c)

   The infrared spectrum of X has a broad absorption between 2500 and 3300 cm⁻¹ and a strong absorption at 1710 cm⁻¹. State what this shows about the functional group in X.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Compound Y has molecular formula C₃H₆O. Its mass spectrum has a molecular ion peak at m/z 58 and a base peak at m/z 43. Y forms an orange precipitate with 2,4-dinitrophenylhydrazine but gives no silver mirror with Tollens' reagent.

   (a)

   What does the reaction with 2,4-dinitrophenylhydrazine and Tollens' reagent show about Y?

   [1 mark]

   • AY is an aldehyde
   • BY is a ketone
   • CY is a carboxylic acid
   • DY is an alcohol

   (b)

   Which fragment ion is responsible for the base peak at m/z 43?

   [1 mark]

   • ACH₃⁺
   • BC₂H₅⁺
   • CCH₃CH₂CO⁺
   • DCH₃CO⁺

   (c)

   State how many peaks there are in the ¹³C NMR spectrum of Y, and explain your answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Compound Z contains only carbon, hydrogen and oxygen, and its molecular ion peak is at m/z 74. Complete combustion of 0.370 g of Z gives 0.660 g of carbon dioxide and 0.270 g of water.

   (a)

   Calculate the empirical formula of Z.

   [3 marks]

   (b)

   The infrared spectrum of Z has a strong absorption at 1745 cm⁻¹ and no absorption between 2500 and 3550 cm⁻¹. The proton NMR spectrum of Z has two peaks, both singlets: δ 2.1 (3H) and δ 3.7 (3H). Deduce the structure of Z, using all the data.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An analytical chemist identifies unknown organic compounds using chemical tests, infrared spectroscopy, mass spectrometry and NMR spectroscopy. In the data below, δ is the chemical shift in ppm.

   (a)

   Two isomers, P and Q, have molecular formula C₃H₇Br. The mass spectrum of each has two molecular ion peaks, at m/z 122 and m/z 124, of almost equal height. The ¹³C NMR spectrum of P has three peaks and that of Q has two peaks. The proton NMR spectrum of Q has a doublet of relative area 6 and a septet of relative area 1. Deduce the structures of P and Q, explaining all the data.

   [6 marks]

   (b)

   Compound R has molecular ion peak at m/z 74 and contains only carbon, hydrogen and oxygen. Its infrared spectrum has a broad absorption at 3300 cm⁻¹ and no absorption near 1700 cm⁻¹. R shows no colour change when warmed with acidified potassium dichromate(VI). Its proton NMR spectrum has two singlets: δ 1.3 (relative area 9) and δ 2.0 (relative area 1). Its ¹³C NMR spectrum has two peaks. Deduce the structure of R, using all the data.

   [6 marks]

   Total for question 4: 12 marks

End of questions