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A-level Chemistry Year 12 · Topic 6

Alkenes, alcohols, analysis and synthesis

Alkenes, alcohols, analysis and synthesis builds your organic chemistry toolkit.

We will study how alkenes react by electrophilic addition, how alcohols are oxidised and dehydrated, and how chemists identify compounds using chemical tests, infrared spectroscopy and mass spectrometry.

Finally we put it all together to plan multi-step synthetic routes between functional groups.

In this topic

  1. 6.1AlkenesFree below · 25 questions
  2. 6.2AlcoholsOpen in Full Marks · 25 questions
  3. 6.3Organic analysisOpen in Full Marks · 59 questions
  4. 6.4Infrared absorption, bond vibrations and the greenhouse effectOpen in Full Marks · 16 questions
  5. 6.5Organic synthesis: reaction pathways and multi-step routes between functional groupsOpen in Full Marks · 21 questions
  6. 6.6Carbonyl compounds: aldehydes and ketones, their reactions and testsOpen in Full Marks · 21 questions
  7. 6.7Carboxylic acids and esters: making acids, their reactions, esterification and hydrolysisOpen in Full Marks · 32 questions
  8. 6.8Nitrogen compounds at AS: primary amines, nitriles and hydroxynitrilesOpen in Full Marks · 22 questions
  9. 6.9Addition polymers: poly(alkenes), PVC, identifying monomers and disposing of polymersOpen in Full Marks · 14 questions

6.1 · Free notes

Alkenes

Diagram: Alkenes

Key points

In more detail

Practice

Alkenes: 10 questions

Pick an answer to check it, or open the answer for the explanation.

1. What type of reaction do alkenes undergo with bromine?

  1. Nucleophilic substitution
  2. Electrophilic addition
  3. Elimination
  4. Free radical substitution
Show answer

B: Electrophilic addition. The pi bond electrons attack the electrophilic bromine molecule.

2. What is the test for an alkene using bromine water?

  1. Turns blue
  2. Orange to colourless
  3. Produces a gas
  4. No change
Show answer

B: Orange to colourless. Alkanes do not decolourise bromine water this way.

3. What type of bond is broken when an alkene reacts with an electrophile?

  1. The sigma bond
  2. The pi bond
  3. An ionic bond
  4. A hydrogen bond
Show answer

B: The pi bond. The weaker pi bond breaks, while the sigma bond remains.

4. According to Markovnikov's rule, the bromine from HBr ends up on:

  1. The more substituted carbon (fewer hydrogens)
  2. The less substituted carbon (more hydrogens)
  3. Either carbon equally
  4. Neither carbon
Show answer

A: The more substituted carbon (fewer hydrogens). The more stable carbocation intermediate directs the major product.

5. What is needed for E/Z isomerism to exist in an alkene?

  1. Both double-bond carbons must have two different groups attached
  2. The alkene must be symmetrical
  3. The molecule must contain a halogen
  4. No rotation must be possible around any bond
Show answer

A: Both double-bond carbons must have two different groups attached. If either carbon has two identical groups, E/Z isomerism isn't possible.

6. What is formed when ethene reacts with steam and a phosphoric acid catalyst?

  1. Ethane
  2. Ethanol
  3. Ethanoic acid
  4. Poly(ethene)
Show answer

B: Ethanol. This is the industrial method of producing ethanol from crude oil derivatives.

7. How many σ and π bonds are there in a molecule of propene, CH₃CH=CH₂?

  1. 9 σ and 1 π
  2. 7 σ and 2 π
  3. 8 σ and 1 π
  4. 6 σ and 1 π
Show answer

C: 8 σ and 1 π. There are 6 C–H σ bonds, 1 C–C σ bond and the σ bond of C=C, giving 8 σ. The C=C double bond also contains one π bond.

8. How many moles of H₂ react fully with 1 mol of buta-1,3-diene (CH₂=CH–CH=CH₂) over a nickel catalyst?

  1. 1
  2. 3
  3. 2
  4. 4
Show answer

C: 2. Each C=C bond adds one H₂. Buta-1,3-diene has two C=C bonds, so it needs 2 mol H₂ to form butane.

9. 2.80 g of ethene (Mᵣ = 28.0) reacts fully with bromine. What mass of 1,2-dibromoethane (Mᵣ = 188) forms?

  1. 18.8 g
  2. 5.6 g
  3. 37.6 g
  4. 9.4 g
Show answer

A: 18.8 g. 2.80 g is 0.100 mol ethene. The ratio is 1:1, so 0.100 mol product has mass 0.100 × 188 = 18.8 g.

10. Which alkene shows E/Z isomerism?

  1. Propene
  2. But-2-ene
  3. 2-methylpropene
  4. But-1-ene
Show answer

B: But-2-ene. Only but-2-ene has two different groups (H and CH₃) on each C=C carbon. The others have two identical groups on one carbon.

Keep going in Full Marks

Full Marks has 25 questions on Alkenes (15 more than here), set out in practice levels. You also get notes and 3D models for all 9 subtopics of Alkenes, alcohols, analysis and synthesis, plus games, timed exams and past papers.

Practise 6.1 in Full MarksOpen Alkenes, alcohols, analysis and synthesis

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