Characteristic organic reactions
Cambridge A-Level Chemistry (9701) · Unit 13: An introduction to AS Level organic chemistry · 9 flashcards
Characteristic organic reactions is topic 13.2 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 13 — An introduction to AS Level organic chemistry , alongside Formulas, functional groups and the naming of organic compounds. In one line: A homologous series is a sequence of organic compounds with the same functional group and similar chemical properties, in which the members differ by a constant structural unit, typically a -CH₂- group.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 9 flashcards — 5 definitions and 4 key concepts — covering the precise wording mark schemes reward. Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Some cards in this deck are on other syllabus topics: 13.3 Shapes of organic molecules; σ and π bonds and 13.4 Isomerism: structural isomerism and stereoisomerism. Each card is labelled with its topic.
'homologous series' in organic chemistry
A homologous series is a sequence of organic compounds with the same functional group and similar chemical properties, in which the members differ by a constant structural unit, typically a -CH₂- group.
What the Cambridge 9701 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Interpret and use these terms for kinds of organic compound and reaction: homologous series; saturated, unsaturated; homolytic and heterolytic fission; free radical; initiation, propagation and termination; electrophile, nucleophile, electrophilic, nucleophilic; addition, elimination, substitution, condensation, hydrolysis; oxidation, reduction. In organic redox equations, [O] may stand for one oxygen atom supplied by an oxidising agent and [H] for one hydrogen atom supplied by a reducing agent.
- Understand and use these terms for types of organic mechanism: free-radical substitution, electrophilic addition, nucleophilic substitution and nucleophilic addition. Mechanisms must show the movement of electron pairs with curly arrows, each starting from a bond or a lone pair.
Also in this deck: 13.3 Shapes of organic molecules; σ and π bonds
- Describe an organic molecule as having a straight chain, a branched chain or a ring (cyclic).
- Describe and explain the shapes and bond angles of molecules that contain sp, sp² or sp³ hybridised atoms.
- Describe how σ and π bonds are arranged in molecules containing sp, sp² or sp³ hybridised atoms.
- Understand the term planar and use it to describe how the atoms are arranged in organic molecules, e.g. ethene.
Also in this deck: 13.4 Isomerism: structural isomerism and stereoisomerism
- Describe structural isomerism, which is divided into chain isomerism, positional isomerism and functional group isomerism.
- Describe stereoisomerism and its two types, geometrical (cis/trans) and optical isomerism (E/Z naming may be used but is not required).
- Describe cis/trans (geometrical) isomerism in alkenes and explain that it arises because π bonds restrict rotation about the C=C bond.
- Explain what a chiral centre is and that each such centre leads to two optical isomers (enantiomers). Appreciate that one compound may contain two or more chiral centres; meso compounds and terms such as diastereoisomers are not required.
- Identify, from a given structural formula (including for cyclic compounds), any chiral centres and any cis/trans (geometrical) isomerism in a molecule.
- Deduce which isomers are possible for an organic molecule whose molecular formula is known.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in these topics
- › Define an addition reaction as one where two or more molecules combine to form a single product.
- › State that sp2 orbitals overlap head-on to form sigma bonds, while p orbitals overlap sideways to form pi bonds.
- › A carbon atom is chiral if it is bonded to four different groups.
- › Check every carbon in a ring for four different groups to find chiral centres, and consider geometric isomerism relative to the ring's plane.
- › Always check for chiral centers in isomerism questions; for instance, 2-methylbutanal has two optical isomers.
Topic 13.2 · Characteristic organic reactions
Define 'homologous series' in organic chemistry.
A homologous series is a sequence of organic compounds with the same functional group and similar chemical properties, in which the members differ by a constant structural unit, typically a -CH₂- group.
Topic 13.2 · Characteristic organic reactions
What is the difference between homolytic and heterolytic fission?
Homolytic fission is the breaking of a covalent bond where each atom takes one electron from the bond, forming free radicals. Heterolytic fission is the breaking of a covalent bond where one atom takes both electrons, forming ions.
Topic 13.2 · Characteristic organic reactions
Define 'nucleophile' and 'electrophile'.
A nucleophile is an electron-rich species that is attracted to a region of positive charge and donates an electron pair to form a covalent bond. An electrophile is an electron-deficient species that is attracted to a region of negative charge and accepts an electron pair to form a covalent bond.
Topic 13.2 · Characteristic organic reactions
Explain the difference between addition, substitution, and elimination reactions.
An addition reaction involves the joining of two or more molecules to form a larger molecule. A substitution reaction involves one atom or group being replaced by another atom or group. An elimination reaction involves the removal of atoms or groups from a molecule, often forming a multiple bond.
Topic 13.3 · Shapes of organic molecules; σ and π bonds
Describe the shape and bond angles in a molecule containing an sp² hybridized carbon atom.
An sp² hybridized carbon atom has a trigonal planar shape with bond angles of approximately 120°. This is due to the three sp² hybrid orbitals repelling each other to maximize separation.
Topic 13.3 · Shapes of organic molecules; σ and π bonds
Describe the arrangement of sigma (σ) and pi (π) bonds in a double bond.
A double bond consists of one sigma (σ) bond and one pi (π) bond. The sigma bond is formed by the direct overlap of orbitals along the internuclear axis, while the pi bond is formed by the sideways overlap of p orbitals above and below the internuclear axis.
Topic 13.4 · Isomerism: structural isomerism and stereoisomerism
What is the difference between structural and stereoisomers?
Structural isomers have the same molecular formula but different structural formulas (different bonding arrangements). Stereoisomers have the same molecular formula and structural formula, but different spatial arrangements of atoms.
Topic 13.4 · Isomerism: structural isomerism and stereoisomerism
Explain why alkenes exhibit geometrical (cis/trans) isomerism.
Alkenes can show geometrical (cis/trans) isomerism because there is restricted rotation about the C=C double bond: the π bond prevents free rotation. Isomerism is only possible when each carbon atom of the C=C carries two different atoms or groups, so the groups can be fixed on the same side (cis) or opposite sides (trans) of the double bond.
Topic 13.4 · Isomerism: structural isomerism and stereoisomerism
What is a chiral center, and what property does it impart to a molecule?
A chiral center is a carbon atom bonded to four different atoms or groups of atoms. The presence of a chiral center makes a molecule chiral, meaning it is non-superimposable on its mirror image, resulting in two optical isomers (enantiomers).
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All Chemistry FlashcardsMore topics in Unit 13 — An introduction to AS Level organic chemistry
Characteristic organic reactions sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Characteristic organic reactions deck
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