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*Revision Materials* 1 Atomic Structure 2 Atoms, molecules and stoichiometry 3 Chemical Bonding 4 States of matter 5 Chemical energetics 6 Electrochemistry 7 Equilibria 8 Reaction kinetics 9 The Periodic Table, chemical periodicity 10 Group 2 11 Group 17 12 Nitrogen and sulfur 13 Organic 14 Hydrocarbons 15 Halogen compounds 16 Hydroxy compounds 17 Carbonyl compounds 18 Carboxylic acids and derivatives 19 Nitrogen compounds 20 Polymerisation 21 Organic synthesis 22 Analytical techniques 23 Chemical energetics 24 Electrochemistry 25 Equilibria 26 Reaction kinetics 27 Group 2 28 Chemistry of transition elements 29 Organic 30 Hydrocarbons 31 Halogen compounds 32 Hydroxy compounds 33 Carboxylic acids and derivatives 34 Nitrogen compounds 35 Polymerisation 36 Organic synthesis 37 Analytical techniques

29 Organic

29.1 Formulas, functional groups and the naming of organic compounds 29.2 Characteristic organic reactions 29.3 Shapes of aromatic organic molecules; σ and π bonds 29.4 Isomerism, optical

Characteristic Organic Reactions

Specification Reference Organic Chemistry, An introduction to A Level organic chemistry 29.2

Quick Notes

  • Electrophilic Substitution: Electrophile replaces a hydrogen atom in an aromatic compound (e.g. nitration of benzene).
CIE A-Level Chemistry diagram showing electrophilic substitution reaction mechanism in benzene.
  • Addition–Elimination: Two-step reaction where a molecule adds to another and a small group is eliminated (e.g. formation of esters and amides).
CIE A-Level Chemistry diagram showing nucleophilic addition–elimination reaction mechanism with acyl chloride.

Full Notes

Electrophilic Substitution

Key point - Electrophiles are electron pair acceptors

Electrophiles are attracted to the high electron density in benzene and this means benzene reacts with electrophiles. Benzene won’t react with nucleophiles (they would be repelled by the high electron density of benzene).

Unlike alkenes, benzene undergoes a substitution reaction with electrophiles rather than addition. This is because the ring of delocalised electrons gets reformed during the mechanism.

Mechanism Overview:

CIE A-Level Chemistry mechanism diagram showing electrophilic substitution in benzene: electrophile attack, loss of H⁺, and ring restoration.

Addition–Elimination

Addition–Elimination occurs when a nucleophile gets added to a compound (often containing a carbonyl group), and a small molecule is eliminated.

Mechanism Overview:

Because of the partially positively charged in the C=O group, carbonyl containing compounds (such as acyl chlorides) react with nucleophiles in addition–elimination.

CIE A-Level Chemistry mechanism diagram showing nucleophilic addition–elimination in an acyl chloride mechanism.

Summary