nucleophilic substitution in halogenoalkanes

• What is a nucleophile?

  A species that donates an electron pair
• How does a nucleophile react with a halogenoalkane?

  It replaces the halogen functional group
• What is the nucleophilic substitution reaction mechanism?

  • Nucleophile approaches halogenoalkane
  • Nucleophile donates electrons to δ+ carbon
  • Original bond breaks heterolytically
  • Halogen departs as halide ion
• What does δ+ indicate in a halogenoalkane?

  A partially positive carbon atom
• What happens to the halogen during nucleophilic substitution?

  It takes both shared electrons and departs
• Which ions can act as nucleophiles in nucleophilic substitution?

  Hydroxide, water, cyanide, ammonia
• What is the result of nucleophilic substitution with hydroxides?

  • Forms alcohols
  • Reaction with aqueous hydroxide ions
  • Example: bromoethane to ethanol
• What is the reaction equation for bromoethane with hydroxide ions?

  CH3CH2Br + OH- ➔ CH3CH2OH + Br-
• What type of reaction is nucleophilic substitution with hydroxides?

  It is a hydrolysis reaction
• Why is the reaction rate slower with water than with hydroxide ions?

  Water is less nucleophilic than hydroxide
• What is the outcome of nucleophilic substitution with cyanide?

  • Forms nitriles
  • Example: bromoethane to ethanenitrile
  • Reaction with ethanolic potassium cyanide
• What is the reaction equation for bromoethane with cyanide ions?

  CH3CH2Br + CN- ➔ CH3CH2CN + Br-
• How does nucleophilic substitution with cyanide affect the carbon chain?

  It extends the carbon chain by one carbon
• What is the result of nucleophilic substitution with ammonia?

  • Forms primary amines
  • Reaction with excess concentrated ammonia
  • Example: bromoethane to ethylamine
• What is the reaction equation for bromoethane with ammonia?

  CH3CH2Br + 2NH3 ➔ CH3CH2NH2 + NH4Br
• What is the mechanism of nucleophilic substitution with ammonia?

  It involves a two-step process
• What happens in the first step of the ammonia substitution reaction?

  Ammonia replaces the bromine atom
• What occurs after ammonia replaces the bromine atom?

  It abstracts a hydrogen from the intermediate
• What is produced alongside the final amine product in the ammonia reaction?

  Ammonium bromide