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CAIE A-Level Chemistry 14.2 Alkenes

Practise alkene preparation, electrophilic addition, oxidation and structural deductions from reaction products.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • select reagents and conditions for addition or oxidation across the C=C bond
  • use curly arrows and intermediates to complete electrophilic-addition mechanisms
  • deduce an alkene structure from oxidative-cleavage products or a multi-step synthesis route

Covered syllabus points

14.2.1—Preparation of alkenes14.2.2—Reactions of alkenes14.2.3—Of aq. bromine to show the presence of a C=C14.2.4—Mechanism: electrophilic addition in alkenes,14.2.5—Inductive effects of alkyl groups

14.2 Alkenes question 1

[Maximum number: 1]

Species such as NH4+,CO32−\mathrm{NH}_{4}{ }^{+}, \mathrm{CO}_{3}{ }^{2-} and PO43−\mathrm{PO}_{4}{ }^{3-} are examples of molecular ions.

OH−(aq)\mathrm{OH}^{-}(\mathrm{aq}) reacts with 2-bromo-2-methylpropane in an SN1\mathrm{S}_{\mathrm{N}} 1 reaction. The molecular ion (CH3)3C+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}^{+}forms as the intermediate in this reaction.

Organic compound M forms when 2-bromo-2-methylpropane is heated with ethanolic OH−\mathrm{OH}^{-}.

Draw the structure of M.

Figure for Question 14.2 Alkenes question 1 — CAIE A-Level Chemistry AS

14.2 Alkenes question 2

[Maximum number: 1]

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

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.

Complete the equation for the reaction of E with cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}) to form F. In the equation, [O][\mathrm{O}] represents cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}).

H2O+[O]+\mathrm{H}_{2} \mathrm{O}+[\mathrm{O}]+

→

14.2 Alkenes question 3

[Maximum number: 4]

4P⃗,Q4 \vec{P}, Q and R all have the molecular formula C3H6O\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}. They are all structural isomers of each other.
P and Q each contain an oxygen atom bonded directly to a carbon atom that is sp2\mathrm{sp}^{2} hybridised. R contains an oxygen atom bonded directly to a carbon atom that is sp3\mathrm{sp}^{3} hybridised.

Question (a)

(a)

R contains two different functional groups, one of which is an alkene group. R reacts with cold, dilute, acidified manganate(VII) ions to form propane-1,2,3-triol.

propane-1,2,3-triol

propane-1,2,3-triol

[ 4 ]

Question (i)

(i)

State the type of reaction and what you would observe when R reacts with bromine water.

[ 2 ]

Question (ii)

(ii)

Draw the structure of the product formed when R reacts with bromine water.

[ 1 ]

Question (iii)

(iii)

Identify the gaseous product formed when R reacts with hot, concentrated, acidified manganate(VII) ions.

[ 1 ]
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