IB Chemistry HL S3.2 Functional groups: classification of organic compounds questions

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Type
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Question 1

Multiple choiceEasy1 mark

In a compound’s ¹H NMR spectrum, the signal from a CH₂ group is a quartet. Assume the splitting is caused by equivalent hydrogen atoms on adjacent carbon atoms. How many equivalent adjacent hydrogen atoms cause the splitting?

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Answer: D. A quartet contains four peaks. When splitting is caused by equivalent hydrogen atoms on adjacent carbon atoms, the number of peaks is one greater than the number of those hydrogen atoms: 4 − 1 = 3.

A: associates no adjacent hydrogen atoms with a quartet; no adjacent hydrogen atoms would give a singlet.
B: associates one adjacent hydrogen atom with a quartet; it gives a doublet.
C: associates two adjacent hydrogen atoms with a quartet; they give a triplet.
Remember: the number of equivalent adjacent hydrogen atoms is one less than the number of peaks.

Question 2

Paper 2Medium6 marks

Two organic compounds, P and Q, are represented by skeletal formulas in Figure 1.

OHPOQ
(a)

State the functional group present in each of P and Q.

[2]
(b)

Determine the molecular formula shared by P and Q.

[1]
(c)

Use Figure 1 and your answer to (b).

(i)

State whether P and Q are saturated or unsaturated.

[1]
(ii)

A student argues that P and Q must belong to the same class of organic compounds because they have the same molecular formula. Explain why this conclusion is not justified.

[2]

Question 3

Paper 2Hard9 marks

A laboratory is checking whether molecular formula alone is sufficient to classify oxygen-containing compounds. Figure 1 shows the structural formulae of four compounds.

ACDBCH3CH2OHCH3OCH2CH3CH3OCH2CH2CH3CH3CH2CH2OH
(a)

Determine the molecular formula of compound A.

[1]
(b)

Using Figure 1, identify two pairs of successive members of homologous series. For each pair, name the series and state the structural change from the smaller member to the larger member.

[4]
(c)

State the general formula for each series identified in (b), using nn for the number of carbon atoms.

[2]
(d)

A technician claims that a molecular formula of C3H8O\mathrm{C_3H_8O} is sufficient to determine uniquely whether a compound belongs to the alcohol or ether series. Evaluate this claim using Figure 1.

[2]

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