CAIE A-Level Chemistry 15. Halogen compounds Question Bank

Practise halogen-compound reactions, mechanisms and conditions, from substitution and elimination to hydrolysis patterns in data.

Covered syllabus points

15.1 Halogenoalkanes

[Maximum number: 1]

Allyl chloride is an important chemical used in the manufacture of plastics, pharmaceuticals and pesticides.

allyl chloride

Allyl chloride can be produced by many different methods. The most common method is chlorination of propene which proceeds via a free-radical substitution mechanism.

Figure for Question 15. Halogen compounds question 1 — CAIE A-Level Chemistry AS

Allyl chloride can also be formed by the following substitution reaction.

Suggest the identity of reagent X.

$\mathrm{SOCl}_{2}$ OR $\mathrm{PCl}_{5}$ OR $\mathrm{PCl}_{3}$ OR $\underline{\mathrm{c}}$ (oncentrated) HCl

[Maximum number: 4]

Species such as $\mathrm{NH}_{4}{ }^{+}, \mathrm{CO}_{3}{ }^{2-}$ and $\mathrm{PO}_{4}{ }^{3-}$ are examples of molecular ions.

(a)

$\mathrm{OH}^{-}(\mathrm{aq})$ reacts with 2-bromo-2-methylpropane in an $\mathrm{S}_{\mathrm{N}} 1$ reaction. The molecular ion $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}^{+}$ forms as the intermediate in this reaction.

[ 4 ]

(i)

Draw the mechanism for the $\mathrm{S}_{\mathrm{N}} 1$ reaction of $\mathrm{OH}^{-}$ with 2-bromo-2-methylpropane. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate. Draw the structures of the organic reactant and organic product.

Figure for Question (i) — CAIE A-Level Chemistry AS

[ 3 ]

Correct SN1 mechanism is shown in the attached official markscheme figure.

Text form of product:
$(\mathrm{CH}_{3})_{3}\mathrm{COH}$

Marking points:
M1 correct dipole on $\delta+\mathrm{C}-\mathrm{Br}^{\delta-}$ in tert-butyl bromide and curly arrow from C-Br to Br.
M2 curly arrow from electron pair on O of $-:\mathrm{OH}$ / $:\mathrm{OH}^{-}$ to $\mathrm{C}^{+}$ in carbocation.
M3 tert-butyl alcohol product.

Figure for Answer to Question (i) — CAIE A-Level Chemistry AS

(ii)

2-bromo-2-methylpropane is a tertiary bromoalkane.

Define tertiary bromoalkane.

[ 1 ]

[Maximum number: 1]

Fig. 4.1 shows how propane, $\mathrm{C}_{3} \mathrm{H}_{8}$ , can be converted to propanoic acid, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}$ .

Fig. 4.1

State the reagent and solvent required for reaction 2 .

[Maximum number: 2]

Fig. 4.1 shows a possible synthesis of propene, $\mathrm{C}_{3} \mathrm{H}_{6}$ .

Fig. 4.1

Reaction 3 is an elimination reaction.

Write an equation for this reaction and identify the solvent and conditions used. equation solvent and conditions

(a)(ii)

$\text { M1 } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{NaOH} \rightarrow \mathrm{C}_{3} \mathrm{H}_{6}+\mathrm{H}_{2} \mathrm{O}+\mathrm{NaCl}$

M2 ethanol (solvent) AND heat / reflux

All question bank results loaded

Covered syllabus points

15. Halogen compounds question 1

15. Halogen compounds question 2

Question (a)

Question (i)

Question (ii)

15. Halogen compounds question 3

15. Halogen compounds question 4