CIE AS Chemistry (9701) exams from 2022

Revision Notes

3.1.6 Terminology Used in Reaction Mechanisms

Terminology Used in Reaction Mechanisms

  • In organic reaction mechanisms, curly arrows represent the movement of electron pairs
  • The arrow beings at a bond or a lone pair of electrons and points to the species that accepts the lone pair of electrons

 

An Introduction to AS Level Organic Chemistry Curly Arrow, downloadable AS & A Level Chemistry revision notes

Curly arrows show electron pairs moving from the source (eg. a nucleophile) to its destination (eg. an electrophile)

Free-radical substitution

  • A free-radical substitution reaction is a reaction in which halogen atoms substitute for hydrogen atoms in alkanes
  • It involves the initiation, propagation and termination steps

 

An Introduction to AS Level Organic Chemistry Free-Radical Substitution, downloadable AS & A Level Chemistry revision notes

Example of a free-radical substitution reaction to form chloromethane from methane

Electrophilic addition

  • An electrophilic addition reaction is a reaction in which an electron rich region in a molecule is attacked by an electrophile (a species that likes electrons/negative charge) followed by the addition of a small molecule to give one product only

 

An Introduction to AS Level Organic Chemistry Electrophilic Addition, downloadable AS & A Level Chemistry revision notes

Example of an electrophilic addition reaction to form ethanol from ethene

Nucleophilic substitution

  • A nucleophilic substitution reaction is a reaction in which an electron-rich nucleophile displaces a halogen atom (the displaced halogen atom is also called the leaving group)

 

An Introduction to AS Level Organic Chemistry Nucleophilic Substitution, downloadable AS & A Level Chemistry revision notes

Example of a nucleophilic substitution reaction to form methanol from chloromethane

Nucleophilic addition

  • A nucleophilic addition reaction is a reaction in which a nucleophile (a species that likes a nucleus/positive charge) attacks an electron-deficient region in a molecule followed by the addition of a small molecule to give one product only

 

An Introduction to AS Level Organic Chemistry Nucleophilic Addition, downloadable AS & A Level Chemistry revision notes

Example of a nucleophilic addition reaction to form propane-2,2-diol from propanone

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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