List the three types of carbocation in order of increasing stability.

Primary < secondary < tertiary.

Why is a tertiary carbocation more stable than a secondary carbocation?

The tertiary carbocation has three alkyl groups attached to the positive carbon, which donate electron density through the inductive effect, stabilising the positive charge more effectively than two alkyl groups.

Why is a secondary carbocation more stable than a primary carbocation?

The secondary carbocation has two alkyl groups donating electron density to stabilise the positive charge, whereas a primary carbocation has only one alkyl group.

AQA A-Level Chemistry 7405

Atomic Structure

Topic overview Fundamental Particles Mass Number and Isotopes Time of Flight Mass Spectrometry: Ionisation and Acceleration Time of Flight Mass Spectrometry: Drift, Detection and Calculating m/z Electron Configuration: Sub-shells and Orbitals Electron Configuration: Writing Configurations for Atoms and Ions Ionisation Energies and Periodic Trends

Amount of Substance

Topic overview Relative Atomic and Molecular Mass The Mole and the Avogadro Constant The Ideal Gas Equation Empirical and Molecular Formula Balanced Equations and Reaction Calculations Atom Economy and Percentage Yield Acid-Base Titrations: Principles, Indicators and Apparatus Acid-Base Titrations: Standard Solutions and Calculations

Bonding

Topic overview Ionic Bonding Covalent, Dative Covalent and Metallic Bonding Crystal Structures: Giant Ionic Lattices and Diamond Crystal Structures: Graphite and Simple Molecular Solids Shapes of Molecules and Ions: VSEPR and Electron Pair Repulsion Shapes of Molecules and Ions: Predicting Shapes and Bond Angles Electronegativity and Bond Polarity Intermolecular Forces

Energetics and Thermodynamics

Topic overview Enthalpy Change and Standard Conditions Calorimetry and Heat Change Calculations Hess's Law and Enthalpy Cycles Mean Bond Enthalpies Lattice Enthalpy and Born-Haber Cycles Enthalpies of Solution and Hydration Entropy Change Gibbs Free Energy and Reaction Feasibility

Kinetics

Topic overview Collision Theory and Activation Energy Maxwell-Boltzmann Distribution and the Effect of Temperature Effect of Concentration and Pressure, and Catalysts Rate Equations: The Rate Equation and Orders of Reaction Rate Equations: The Effect of Concentration on Rate The Rate Constant and the Arrhenius Equation Determining Rate Equations: The Initial Rates Method Determining Rate Equations: Continuous Monitoring Rate Equations and Reaction Mechanisms

Chemical Equilibria

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Redox and Electrochemistry

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Acids and Bases

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Periodicity and Group Chemistry

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Period 3 Elements and Their Oxides

Topic overview Reactions of Na and Mg with Water Period 3 Elements with Oxygen: The Oxides Formed and Their Bonding Period 3 Elements with Oxygen: Structures and Oxidation States Melting Points of Period 3 Oxides Period 3 Oxides with Water: Sodium and Magnesium Oxides Period 3 Oxides with Water: The Acidic Oxides and the pH Trend Period 3 Oxides with Acids and Bases: The Reactions Period 3 Oxides with Acids and Bases: Acidic, Basic and Amphoteric

Transition Metals

Topic overview General Properties of Transition Metals Complex Ions: Ligands, Coordinate Bonds and Denticity Complex Ions: Why a Species Can Act as a Ligand, and Coordination Number Substitution Reactions with Monodentate Ligands Substitution Reactions with Bidentate and Multidentate Ligands Haemoglobin and the Chelate Effect Shapes of Complex Ions and Stereoisomerism Formation of Coloured Ions and the d-d Transition Colorimetry and Concentration Determination Variable Oxidation States and Vanadium Chemistry Tollens' Reagent and Redox Titrations Heterogeneous Catalysis Vanadium(V) Oxide and the Contact Process Homogeneous Catalysis and Autocatalysis Metal-Aqua Ions and Acidity Metal Aqua Ions with Bases: Reactions with Hydroxide and Ammonia Metal Aqua Ions with Bases: Why They React, and Their Equations Amphoteric Hydroxides Identifying Transition Metal Ions by Test-Tube Reactions

Introduction to Organic Chemistry

Topic overview Nomenclature and Formula Representations Homologous Series and General Formulae IUPAC Naming: Stems, Prefixes and Suffixes Free Radical and Curly Arrow Mechanisms Structural Isomerism E-Z Stereoisomerism and CIP Priority Rules Chirality and Enantiomers Racemic Mixtures and Optical Activity

Hydrocarbons

Topic overview Alkanes, Fractional Distillation and Cracking Combustion of Alkanes and Pollutants Free Radical Chlorination of Alkanes Alkenes: Structure, Bonding and Electrophilic Addition Markovnikov's Rule and Carbocation Stability Addition Polymers and Repeating Units Properties and Uses of Polyalkenes

Halogenoalkanes, Alcohols and Organic Analysis

Topic overview Nucleophilic Substitution of Halogenoalkanes Effect of Bond Enthalpy on Reaction Rate Elimination Reactions and Competing Mechanisms CFCs and Ozone Depletion Industrial Production of Alcohols Biofuels and Carbon Neutrality Classification and Oxidation of Alcohols Distinguishing Aldehydes and Ketones Elimination of Water from Alcohols Test-Tube Reactions for Functional Groups Mass Spectrometry and Molecular Formula Infrared Spectroscopy, Functional Groups and Global Warming

Carbonyls, Carboxylic Acids and Derivatives

Topic overview Oxidation of Aldehydes and Distinguishing Tests Reduction of Carbonyls with NaBH4 Nucleophilic Addition with KCN and Hydroxynitrile Formation Hazards of KCN and Formation of Enantiomers Structure and Acidity of Carboxylic Acids Esterification and the Uses of Esters Vegetable Oils, Fats and the Hydrolysis of Esters Soap and Biodiesel Production from Fats Structure of Acid Anhydrides, Acyl Chlorides and Amides Nucleophilic Addition-Elimination Reactions of Acyl Chlorides Acid Anhydrides and the Industrial Synthesis of Aspirin Purifying organic solids and liquids

Aromatic Chemistry and Amines

Topic overview Bonding and Stability of Benzene Electrophilic Substitution: Nitration Electrophilic Substitution: Friedel-Crafts Acylation Preparation of Aliphatic and Aromatic Amines Base Strength of Amines Amines as Nucleophiles, and Quaternary Ammonium Salts Amines with Acyl Chlorides and Acid Anhydrides

Polymers, Amino Acids, Proteins and DNA

Topic overview Condensation Polymers: Polyesters Condensation Polymers: Polyamides Intermolecular Forces in Condensation Polymers Biodegradability and Disposal of Polymers Amino Acids and Zwitterions Peptide Bonds and Protein Structure Hydrogen Bonding and Disulfide Bridges in Proteins Hydrolysis of Proteins and TLC Identification Enzymes, Active Sites and Inhibitors in Drug Design DNA: Nucleotides, the Double Helix and Base Pairing Cisplatin and Anticancer Drug Action

Organic Synthesis, NMR and Chromatography

Topic overview Multi-Step Synthesis Routes Green Chemistry Principles in Synthesis Design Principles of NMR and the Delta Scale Carbon-13 NMR Interpretation Proton NMR Chemical Shift and Integration Spin-Spin Splitting and the n+1 Rule TMS and Deuterated Solvents Thin-Layer Chromatography and Rf Values Column and Gas Chromatography, and GC-MS

Hydrocarbons

Markovnikov's Rule and Carbocation Stability

3 things to know
Papers 2 and 3

Overview

Primary, secondary and tertiary carbocations, and predicting the major product.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What does Markovnikov's rule predict about the addition of HBr to an unsymmetrical alkene?

Who and when

In the addition of HBr to propene, which carbon atom does the hydrogen atom bond to according to Markovnikov's rule?

Key term

What is a carbocation?

Questions from this subtopic

Each one with the model answer underneath.

1
What does Markovnikov's rule predict about the addition of HBr to an unsymmetrical alkene?
Model answer
The hydrogen atom adds to the carbon atom of the double bond that already has more hydrogen atoms attached.
2
In the addition of HBr to propene, which carbon atom does the hydrogen atom bond to according to Markovnikov's rule?
Model answer
The hydrogen bonds to the terminal carbon (C-1), which already has two hydrogen atoms attached.
3
What is a carbocation?
Model answer
A positively charged carbon species formed as an intermediate during electrophilic addition reactions.
4
List the three types of carbocation in order of increasing stability.
Model answer
Primary < secondary < tertiary.
5
Why is a tertiary carbocation more stable than a secondary carbocation?
Model answer
The tertiary carbocation has three alkyl groups attached to the positive carbon, which donate electron density through the inductive effect, stabilising the positive charge more effectively than two alkyl groups.
6
Why is a secondary carbocation more stable than a primary carbocation?
Model answer
The secondary carbocation has two alkyl groups donating electron density to stabilise the positive charge, whereas a primary carbocation has only one alkyl group.

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