5.4.2

Reactions of Alkenes

Test yourself on Reactions of Alkenes

After reading these notes, test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Alkenes

Alkenes are molecules with a double covalent bond. There is a high electron density between the carbon atoms because of the double bond.

Reactions of alkenes

Reactions of alkenes

  • Alkenes react with several reagents in addition reactions.
  • The alkenes are nucleophiles because of the high electron density between the carbon atoms.
  • The mechanism is shown next for the reaction with hydrogen bromide.
  • The mechanism is called the electrophilic addition mechanism (because an electrophile is added).
  • They will react in a similar way with sulfuric acid, and bromine.
Electrophilic addition

Electrophilic addition

  • Above shows the reaction with HBr.
With bromine

With bromine

  • The reaction can also be done with Br2.
  • The partial charges are assigned to the bromine atoms because the high electron density of the double bond repels the bonding electrons and polarises the bond - this is shown in the mechanism.

Uses of Electrophilic Addition

Electrophilic addition reactions between alkenes and bromine as well as alkenes and sulfuric acid are useful.

With bromine

With bromine

  • The reaction with bromine is used as a test for alkenes.
    • Bromine water is a light orange colour and will be decolourised in the presence of an alkene (light orange → colourless).
  • This test works because bromine can add to alkenes via an electrophilic addition reaction.
With sulfuric acid

With sulfuric acid

  • The reaction with sulfuric acid is used to produce alcohols.
    • The sulfate ion is removed by nucleophilic substitution.

Asymmetric Electrophilic Addition

Asymmetric alkenes can have multiple products in electrophilic addition reactions.

Multiple products

Multiple products

  • If you have an asymmetric alkene, you can get multiple products.
    • A reaction will favour one of the products over the other - we call this selectivity.
  • This is shown for the reaction of propene with HBr.
Intermediate stability

Intermediate stability

  • This selectivity is driven by carbocation intermediate stability:
    • Tertiary carbocations > secondary carbocations > primary carbocations.
  • The more alkyl groups there are next to the positive charge, the more stable the intermediate is.
    • Alkyl groups push electrons and so help to stabilise adjacent positive charge.
Which product when?

Which product when?

  • When considering which product is most likely, we must consider the intermediates formed.
  • 2-bromopropane is the most likely product because the intermediate is a secondary carbocation, rather than a primary carbocation.
    • This is because the secondary carbocation is more stable.
      • It has more alkyl groups pushing electrons onto the positive charge.
  • Both reactions will happen and you will get both products, but you will have one major and one minor.
Jump to other topics
1

Physical Chemistry

1.1

Atomic Structure

1.1.1Fundamental Particles1.1.2Isotopes & Mass Number1.1.3Mass Spectrometry1.1.4Electron Shells, Sub-Shells & Orbitals1.1.5Electron Configuration1.1.6Ionisation Energy1.1.7Factors Affecting Ionisation Energies1.1.8Trends of Ionisation1.1.9Specific Impacts on Ionisation Energies1.1.10End of Topic Test - Atomic Structure1.1.11A-A* (AO3/4) - Atomic Structure
1.2

Amount of Substance

1.2.1Relative Masses1.2.2The Mole1.2.3The Ideal Gas Equation1.2.4Empirical & Molecular Formulae1.2.5Balanced Equations1.2.6Percentage Yield1.2.7A-A* (AO3/4) - Percentage Yield1.2.8Atom Economy1.2.9End of Topic Test - Amount of Substance1.2.10A-A* (AO3/4) - Substances & Yield1.2.11Diagnostic Misconceptions - Moles
1.3

Bonding

1.3.1Ionic Bonding1.3.2Covalent & Dative Bonding1.3.3Carbon Structures1.3.4Metallic Bonding1.3.5Physical Properties1.3.6Shapes of Molecules1.3.7Polarity1.3.8Intermolecular Forces1.3.9Intermolecular Forces 21.3.10End of Topic Test - Bonding1.3.11Exam-Style Question - Shape of Molecules1.3.12A-A* (AO3/4) - Bonding1.3.13Diagnostic Misconceptions - Ions1.3.14Diagnostic Misconceptions - Ionic & Covalent1.3.15Diagnostic Misconceptions - Phase Change1.3.16Diagnostic Misconceptions - Boiling1.3.17Diagnostic Misconceptions - Polar Bonds
1.4

Energetics

1.4.1Enthalpy Changes1.4.2Bond Breaking and Making1.4.3Enthalpy Changes: Standard Conditions1.4.4Calorimetry1.4.5Hess' Law1.4.6Bond Enthalpies1.4.7End of Topic Test - Energetics1.4.8Diagnostic Misconceptions - Calorimetry
1.5

Kinetics

1.5.1Collision Theory1.5.2Maxwell-Boltzmann Distribution1.5.3Increasing Rates1.5.4End of Topic Test - Kinetics
1.6

Equilibria

1.6.1Le Chatelier1.6.2Equilibrium Constants1.6.3A-A* (AO3/4) - Energetics, Kinetics, Equilibria1.6.4End of Topic Test - Equilibria1.6.5Diagnostic Misconceptions - Solids
1.7

Redox

1.7.1Redox1.7.2End of Topic Test - Redox
2

Physical Chemistry 2 (A2 Only)

2.1

Thermodynamics (A2 Only)

2.1.1Born-Haber Cycles (A2 Only)2.1.2Born-Haber Cycle Calculations (A2 Only)2.1.3Entropy (A2 Only)2.1.4Free Energy (A2 Only)2.1.5End of Topic Test - Thermodynamics2.1.6A-A* (AO3/4) - Thermodynamics
2.2

Rate Equations (A2 Only)

2.2.1Rate Equations (A2 Only)2.2.2Rate Equations 2 (A2 Only)2.2.3The Arrhenius Equation (A2 Only)2.2.4Experimental Methods for Rates (A2 Only)2.2.5End of Topic Test - Rate Equations2.2.6Exam-Style Question - Rates2.2.7A-A* (AO3/4) - Rate Equations
2.3

The Equilibrium Constant Kp (A2 Only)

2.3.1Properties of Kp (A2 Only)
2.4

Electrochemical Cells (A2 Only)

2.4.1Electrochemical Cells (A2 Only)2.4.2Electrochemical Series (A2 Only)2.4.3Commercial Application (A2 Only)2.4.4End of Topic Test - Kp & Electrochemistry2.4.5A-A* (AO3/4) - Electrochemical Cells2.4.6Diagnostic Misconceptions - Salt Bridges2.4.7Diagnostic Misconceptions - Electrode, Electrolyte
2.5

Acids & Bases (A2 Only)

2.5.1Brønsted-Lowry Acids & Bases (A2 Only)2.5.2pH (A2 Only)2.5.3The Ionic Product of Water (A2 Only)2.5.4Weak Acids & Bases (A2 Only)2.5.5pH Curves & Titrations (A2 Only)2.5.6pH Curves & Titrations 2 (A2 Only)2.5.7Buffer Solutions (A2 Only)2.5.8End of Topic Test - Acids & Bases2.5.9Exam-Style Question - Weak Acids2.5.10A-A* (AO3/4) - Acids & Bases2.5.11Diagnostic Misconceptions - Ammonia is an Alkali2.5.12Diagnostic Misconceptions - Water's Neutrality2.5.13Diagnostic Misconceptions - Concentrate & Strength
3

Inorganic Chemistry

3.1

Periodicity & Trends

3.1.1The Periodic Table3.1.2Trends in the Periodic Table3.1.3End of Topic Test - Periodicity & Trends3.1.4Diagnostic Misconceptions - Atomic Radius
3.2

Group 2

3.2.1Group 2 Chemistry3.2.2End of Topic Test - Group 2
3.3

Group 7

3.3.1Introduction to Halogens3.3.2Reactions of Halogens3.3.3Chlorine & Chlorate(I)3.3.4End of Topic Test - Group 73.3.5Exam-Style Question - Group 73.3.6A-A* (AO3/4) - Periodicity, Group 2 & 7
4

Inorganic Chemistry 2 (A2 Only)

4.1

Period 3 (A2 Only)

4.1.1Period 3 Elements & Oxides (A2 Only)4.1.2Period 3 Oxides (A2 Only)4.1.3End of Topic Test - Period 3
4.2

Transition Metals (A2 Only)

4.2.1General Properties (A2 Only)4.2.2Substitution Reactions (A2 Only)4.2.3Shapes of Complex Ions (A2 Only)4.2.4Colours of Ions (A2 Only)4.2.5Variable Oxidation States (A2 Only)4.2.6Titrations (A2 Only)4.2.7Homogeneous Catalysts (A2 Only)4.2.8Heterogeneous Catalysts (A2 Only)4.2.9End of Topic Test - Transition Metals4.2.10A-A* (AO3/4) - Transition Metals
4.3

Reactions of Ions in Aqueous Solutions (A2 Only)

4.3.1Acidity (A2 Only)4.3.2Identification (A2 Only)4.3.3End of Topic Test - Reactions of Ions in Solution
5

Organic Chemistry 1

5.1

Introduction

5.1.1Naming Conventions5.1.2Mechanism5.1.3Isomerism5.1.4End of Topic Test - Introduction to Organic Chem
5.2

Alkanes

5.2.1Fractional Distillation5.2.2Cracking5.2.3Combustion5.2.4Chlorination5.2.5End of Topic Test - Alkanes
5.3

Halogenoalkanes

5.3.1Substitution Reactions5.3.2Elimination Reactions5.3.3Ozone Depletion5.3.4End of Topic Test - Halogenoalkanes
5.4

Alkenes

5.4.1Introduction to Alkenes5.4.2Reactions of Alkenes5.4.3Polymerisation Reactions5.4.4Properties of Polymers5.4.5End of Topic Test - Alkenes
5.5

Alcohols

5.5.1Production of Alcohols5.5.2Oxidation of Alcohols5.5.3Oxidation of Alcohols - 25.5.4Elimination Reactions5.5.5End of Topic Test - Alcohols5.5.6Exam-Style Question - Alcohols
5.6

Organic Analysis

5.6.1Reactions5.6.2Reactions 25.6.3Mass Spectrometry5.6.4Infrared Spectroscopy5.6.5End of Topic Test - Organic Analysis
5.7

A-A* (AO3/4) - Organic 1

5.7.1A-A* (AO3/4) - Organic 1
6

Organic Chemistry 2 (A2 Only)

6.1

Optical Isomerism (A2 Only)

6.1.1Optical Isomerism (A2 Only)6.1.2End of Topic Test - Optical Isomerism
6.2

Aldehydes & Ketones (A2 Only)

6.2.1Aldehydes & Ketones (A2 Only)6.2.2End of Topic Test - Aldehydes & Ketones
6.3

Carboxylic Acids & Esters (A2 Only)

6.3.1Acids & Esters (A2 Only)6.3.2Acylation (A2 Only)6.3.3End of Topic Test - Carboxylic Acids & Esters
6.4

Aromatic Chemistry (A2 Only)

6.4.1Structure & Reactivity (A2 Only)6.4.2Reactions of Benzene (A2 Only)6.4.3End of Topic Test - Aromatic Chemistry
6.5

Amines (A2 Only)

6.5.1Nature & Preparation of Amines (A2 Only)6.5.2Basicity & Nucleophilicity (A2 Only)6.5.3End of Topic Test - Amines
6.6

Polymers (A2 Only)

6.6.1Condensation Polymers (A2 Only)6.6.2Biodegradability (A2 Only)
6.7

Biological Organic (A2 Only)

6.7.1Amino Acids (A2 Only)6.7.2Proteins (A2 Only)6.7.3DNA (A2 Only)6.7.4Anti-Cancer Drugs (A2 Only)6.7.5End of Topic Test - Biological Organic
6.8

Organic Synthesis (A2 Only)

6.8.1Organic Synthesis (A2 Only)6.8.2Examples of Synthetic Routes (A2 Only)6.8.3End of Topic Test - Polymers & Organic Synthesis
6.9

NMR Spectroscopy (A2 Only)

6.9.1Understanding NMR (A2 Only)6.9.2Carbon-13 NMR (A2 Only)6.9.3Hydrogen-1 NMR (A2 Only)6.9.4Hydrogen-1 NMR 2 (A2 Only)6.9.5End of Topic Test - NMR
6.10

Chromatography (A2 Only)

6.10.1Overview of Chromatography (A2 Only)6.10.2Thin-Layer Chromatography (A2 Only)6.10.3Column Chromatography (A2 Only)6.10.4Gas Chromatography (A2 Only)6.10.5End of Topic Test - Chromatography
6.11

A-A* (AO3/4) - Organic 2

6.11.1A-A* (AO3/4) - Organic 2

Practice questions on Reactions of Alkenes

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What is a typical reaction for alkenes?Multiple choice
  2. 2
    Which of the following is true for alkenes?True / false
  3. 3
    What must be reacted together to give dibromopropane?Fill in the list
  4. 4
    What is the end product in the sulfuric acid and alkene reaction (after water is added)?Multiple choice
  5. 5
    What is produced by the reaction between an alkene and a Br<sub>2</sub> molecule?Multiple choice
Answer all questions on Reactions of Alkenes

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium

Introduction to Alkenes

Polymerisation Reactions