OZ8: Nucleophilic Substitution Flashcards
Define “nucleophile” (3)
- A molecule or negatively charged ion
- with a lone pair of electrons it can donate to a positively charged atom
- to form a covalent bond
Define “substitution”
A reaction in which one atom or group in a molecule is replaced by another atom or group
Give the general formula for the nucleophilic substitution reaction between a haloalkane and OH- ions.
R-X + NaOH ====> ROH + NaX
Describe the nucleophilic substitution reaction between a haloalkane and OH- ions.(3)
- The nucleophile OH- attacks the electron deficient carbon atom in the C-halogen polar bond
- The OH- donates 2 electrons to form a new dative covalent bond
- The C-halogen bond breaks heterolytically and the halogen atom receives 2 electrons - produces a halide ion (leaving group)
What conditions does the nucleophilic substitution reaction between a haloalkane and OH- ions need? (2)
- Warm aqueous sodium hydroxide
- Heat under reflux
Give the general formula for the nucleophilic substitution reaction between a haloalkane and water.
R-X + H2O ===> R-OH + H+ + X-
What conditions does the nucleophilic substitution reaction between a haloalkane and water need?
Heating the two substances together under reflux
Describe the nucleophilic substitution reaction between a haloalkane and water.(4)
- The nucleophile H2O attacks the electron deficient carbon atom in the C-halogen polar bond
- The H2O donates 2 electrons to form a new dative covalent bond
- The C-halogen bond breaks heterolytically and the halogen atom receives 2 electrons - produces a halide ion (leaving group) and an intermediate forms with an oxygen that has 3 bonds.
- This is unstable so one OH bond breaks and an alcohol is formed alongside the halide ion and H+ that has left
Give the general formula for the nucleophilic substitution reaction between a haloalkane and ammonia.
R-X + NH3 ===> R-NH3 + X- R-NH2 + X- + NH4+
What conditions does the nucleophilic substitution reaction between a haloalkane and ammonia need?
The haloalkane needs to be heated in a sealed tube with excess ethanolic ammonia
Describe the nucleophilic substitution reaction between a haloalkane and ammonia.
- The nucleophile ammonia attacks the electron deficient carbon atom in the C-halogen polar bond
- The ammonia donates 2 electrons to form a new dative covalent bond
- The C-halogen bond breaks heterolytically and the halogen atom receives 2 electrons - produces a halide ion (leaving group) and an intermediate forms with a nitrogen that has 4 bonds.
- This is unstable so one NH bond breaks and a hydrogen is removed by an ammonia molecule
- This leaves an amine
What is an amine?
An organic compound based on ammonia but with 1 or more of the hydrogen atoms replaced by an alkyl group
What nucleophilic substitution reaction produces a haloalkane?
A nucleophilic substitution reaction between a halide ion (X-) and an alcohol
What is a nucleophilic substitution reaction producing a haloalkane from an alcohol done in the presence of?
A strong acid
Why is a nucleophilic substitution reaction producing a haloalkane from an alcohol done in the presence of a strong acid?
Gives the carbon atom to which the oxygen is attached in the alcohol a higher partial positive charge, allowing it to be more readily attacked by halide ions