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.
'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
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- interpret and use the following terminology associated with types of organic compounds and reactions: (a) homologous series (b) saturated and unsaturated (c) homolytic and heterolytic fission (d) free radical, initiation, propagation, termination (e) nucleophile, electrophile, nucleophilic, electrophilic (f) addition, substitution, elimination, hydrolysis, condensation (g) oxidation and reduction (in equations for organic redox reactions, the symbol [O] can be used to represent one atom of oxygen from an oxidising agent and the symbol [H] to represent one atom of hydrogen from a reducing agent)
- understand and use the following terminology associated with types of organic mechanisms: (a) free-radical substitution (b) electrophilic addition (c) nucleophilic substitution (d) nucleophilic addition (in organic reaction mechanisms, the use of curly arrows to represent movement of electron pairs is expected; the arrow should begin at a bond or a lone pair of electrons)
- describe organic molecules as either straight-chained, branched or cyclic
- describe and explain the shape of, and bond angles in, molecules containing sp, sp2 and sp3 hybridised atoms
- describe the arrangement of σ and π bonds in molecules containing sp, sp2 and sp3 hybridised atoms
- understand and use the term planar when describing the arrangement of atoms in organic molecules, for example ethene
- describe structural isomerism and its division into chain, positional and functional group isomerism
- describe stereoisomerism and its division into geometrical (cis/trans) and optical isomerism (use of E/Z nomenclature is acceptable but is not required)
- describe geometrical (cis/trans) isomerism in alkenes, and explain its origin in terms of restricted rotation due to the presence of π bonds
- explain what is meant by a chiral centre and that such a centre gives rise to two optical isomers (enantiomers)
- identify chiral centres and geometrical (cis/trans) isomerism in a molecule of given structural formula including cyclic compounds
- deduce the possible isomers for an organic molecule of known molecular formula
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 Characteristic organic reactions
- › Carefully trace the carbon skeleton after oxidation; a carbon atom becomes chiral if it is bonded to four different groups.
- › The 'horseshoe' in the intermediate must represent the delocalized system and must not include the sp3 carbon being substituted.
- › Define an addition reaction as one where two or more molecules combine to form a single product.
- › In nucleophilic addition, ensure the curly arrow starts from the lone pair on the Carbon atom of the cyanide ion.
- › State that sp2 orbitals overlap head-on to form sigma bonds, while p orbitals overlap sideways to form pi bonds.
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.
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.
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.
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.
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.
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.
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.
Explain why alkenes exhibit geometrical (cis/trans) isomerism.
Alkenes exhibit geometrical isomerism due to the restricted rotation around the carbon-carbon double bond. The pi (π) bond prevents free rotation, leading to different spatial arrangements of substituents on either side of the double bond.
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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