Nucleophilic Substitution of Haloalkanes (OCR A Level Chemistry)

Revision Note

Test yourself
Philippa

Author

Philippa

Last updated

Nucleophilic Substitution of Haloalkanes

Nucleophiles 

  • nucleophile is an electron-rich species that can donate a pair of electrons
    • ‘Nucleophile’ means ‘nucleus/positive charge loving’ as nucleophiles are attracted to positively charged species
    • Nucleophilic refers to reactions that involve a nucleophile

  • There are various different species which can behave as nucleophiles, and some make better nucleophiles than others

Halogen Compounds Nucleophilicity, downloadable AS & A Level Chemistry revision notes

A hydroxide ion is a better nucleophile as it has a full formal negative charge whereas the oxygen atom in water only carries a partial negative charge

  • nucleophilic substitution reaction is one in which a nucleophile attacks a carbon atom which carries a partial positive charge
  • An atom that has a partial negative charge is replaced by the nucleophile
  • Haloalkanes will undergo nucleophilic substitution reactions due to the polar C-X bond (where X is a halogen)

Halogen Compounds Polarity of the C-X bond, downloadable AS & A Level Chemistry revision notes

Due to large differences in electronegativity between the carbon and halogen atom, the C-X bond is polar

General nucleophilic substitution mechanism, downloadable AS & A Level Chemistry revision notes

General Mechanism for Nucleophilic Substitution

Hydrolysis of Haloalkanes 

  • The nucleophile in this reaction is the hydroxide, OH- ion
  • An aqueous solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH) with ethanol is used
  • This reaction is very slow at room temperature, so the reaction mixture is warmed
  • This is an example of a hydrolysis reaction and the product is an alcohol
  • The rate of this reaction depends on the type of halogen in the haloalkane 

  • The stronger the C-X bond, the slower the rate of the reaction
  • In terms of bond enthalpy, C-F > C-Cl > C-Br > C-I
  • Fluoroalkanes do not react at all, but iodoalkanes have a very fast rate of reaction

The nucleophilic substitution mechanisms for the above reactions are as follows:

Nucleophilic Substitution with OH-

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.