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CAIE A-Level Chemistry 22.1 Infrared Spectroscopy

Practise matching infrared absorptions to bonds and functional groups and using missing peaks to reject structures.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • match a significant absorption range to both its bond and the functional group containing it
  • combine several diagnostic peaks such as C=O, C–O, O–H, C=C or C≡N before identifying a compound
  • use the absence of an expected diagnostic absorption as evidence against a proposed structure

Covered syllabus points

22.1.1—Analyse an infrared spectrum of a simple

22.1 Infrared spectroscopy question 1

[Maximum number: 3]

Organic compounds can be distinguished using chemical tests and analytical techniques.

Question (a)

(a)

Organic compound E contains three carbon atoms. E reacts with cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}) to form a single compound F with Mr=154.9M_{\mathrm{r}}=154.9.
Fig. 3.1 shows the infrared spectrum of E.
Fig. 3.2 shows the infrared spectrum of F.

Fig. 3.1

Fig. 3.1

Fig. 3.2

Fig. 3.2

Table 3.2

Table 3.2

Both spectra show absorptions between 2850 and 2950 cm−12950 \mathrm{~cm}^{-1} owing to C-H bonds in each molecule.

[ 3 ]

Question (i)

(i)

Use the two infrared spectra and Table 3.2 to identify the functional group present only in E.
Explain your answer, referring only to absorptions at frequencies greater than 1500 cm−11500 \mathrm{~cm}^{-1}.
functional group explanation

[ 1 ]

Question (ii)

(ii)

Use the infrared spectrum of F to identify the functional group formed when E reacts with cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}).
Explain your answer, referring only to absorptions at frequencies greater than 1500 cm−11500 \mathrm{~cm}^{-1}.
functional group explanation

[ 1 ]

Question (iii)

(iii)

Use the information in 3(c) to suggest a structure for E.

[ 1 ]
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