29.2 A2 Level

Characteristic organic reactions

9 flashcards to master this topic

Definition Flip

Define electrophilic substitution, including the role of the electrophile.

Answer Flip

Electrophilic substitution is a reaction where an electrophile (electron-seeking species) replaces an atom or group in a molecule. The electrophile is attracted to an area of high electron density and forms a covalent bond, displacing another group.

Example: Nitration of benzene.
Key Concept Flip

Describe the structure and bonding in benzene, including reference to sp² hybridisation and the delocalised π system.

Answer Flip

Benzene has a planar, cyclic structure with each carbon atom sp² hybridised. Each carbon forms three sigma (σ) bonds (two to adjacent carbons and one to a hydrogen). The remaining p-orbital on each carbon overlaps sideways, forming a delocalised π system above and below the plane of the ring.

Definition Flip

What are enantiomers, and what is their key characteristic regarding plane-polarised light?

Answer Flip

Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They have identical physical and chemical properties, except for their ability to rotate plane-polarised light in opposite directions.

Definition Flip

Define 'optically active' and 'racemic mixture'.

Answer Flip

A substance is optically active if it rotates the plane of polarised light. A racemic mixture is an equimolar mixture of two enantiomers; it shows no overall rotation of plane-polarised light because the rotations cancel each other out.

Key Concept Flip

Describe the effect of individual optical isomers on plane polarised light.

Answer Flip

Each optical isomer of a single substance rotates plane polarised light. One enantiomer rotates the light clockwise (dextrorotatory, +), while the other rotates it anticlockwise (laevorotatory, -) by the same amount.

Key Concept Flip

Explain why the different enantiomers of a drug molecule might exhibit different biological activity.

Answer Flip

Enantiomers interact differently with chiral biological receptors (

Example: enzymes, proteins) in the body. One enantiomer might fit the active site and exhibit a therapeutic effect, while the other enantiomer might not fit or might even cause unwanted side effects.
Key Concept Flip

Why is it sometimes necessary to separate a racemic mixture of a drug into pure enantiomers?

Answer Flip

Separating a racemic mixture is important if only one enantiomer has the desired therapeutic effect and the other is inactive or harmful. Administering only the active enantiomer reduces dosage and minimises potential side effects.

Example: Thalidomide
Key Concept Flip

Explain how chiral catalysts can be used to produce a single pure optical isomer.

Answer Flip

Chiral catalysts have a chiral environment that selectively favours the formation of one enantiomer over the other during a reaction. This results in the synthesis of a single, pure optical isomer, rather than a racemic mixture, improving drug efficacy and safety.

Key Concept Flip

Explain the difference between addition-elimination and electrophilic substitution mechanisms.

Answer Flip

Electrophilic substitution involves the replacement of an atom or group by an electrophile, commonly seen in aromatic compounds. Addition-elimination involves the addition of a nucleophile to a carbonyl compound followed by the elimination of a leaving group, forming a new carbonyl compound derivative.

Example: Acylation of acyl chlorides.

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29.1 Formulas, functional groups and the naming of organic compounds 30.1 Arenes