4861066
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Mind Map by Bee Brittain, updated more than 1 year ago
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Created by Bee Brittain
over 10 years ago
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15.1 The Chemistry of the Haloalkanes
- Reactivity of The Haloalkanes
- Halogen atoms are more electronegative than carbon atoms
- This means the carbon-halogen bond is Polar
- Carbon atom has slightly positive charge
- Attract species that donate a pair of electrons = NUCLEOPHILES
- NUCLEOPHILE = Electron pair donor
- Hydroxide Ions = :OH-
- Water molecules = H2O:
- Ammonia Molecules = :NH3
- When a Haloalkane reacts with a nucleophile, the
nucleophile replaces the hydrogen in a Substitution
Reaction
- New Compound produced with a different functional group.
- NUCLEOPHILIC SUBSTITUTION
- NUCLEOPHILIC SUBSTITUTION
- New Compound produced with a different functional group.
- NUCLEOPHILE = Electron pair donor
- Attract species that donate a pair of electrons = NUCLEOPHILES
- This means the carbon-halogen bond is Polar
- Halogen atoms are more electronegative than carbon atoms
- NUCLEOPHILIC SUBSTITUTION
- Hydrolysis
- Halogen atom is replaced by an -OH group.
- 1) Nucleophile (OH-) approaches
the C atom attached to the halogen
on the OPPOSITE side of the
molecule from the halogen atom
- 2) Direction of attack of OH- ion minimises
repulsion between the nucleophile and the
slightly negative halogen atom
- 3) Lone pair of electrons on the hydroxide ion are attracted
and donated to the slightly positive carbon atom
- 4) New bond formed between the Oxygen
atom of the hydroxide ion and the carbon
atom
- 5) The carbon-halogen bond is
broken by heterolytic fission
- 6) The new organic product is an alcohol
(when OH- nucleophile used). A halide ion is
also formed
- 6) The new organic product is an alcohol
(when OH- nucleophile used). A halide ion is
also formed
- 5) The carbon-halogen bond is
broken by heterolytic fission
- 4) New bond formed between the Oxygen
atom of the hydroxide ion and the carbon
atom
- 3) Lone pair of electrons on the hydroxide ion are attracted
and donated to the slightly positive carbon atom
- 2) Direction of attack of OH- ion minimises
repulsion between the nucleophile and the
slightly negative halogen atom
- Haloalkanes can be converted to alcohols using aqueous sodium hydroxide
- Very slow reaction at Rtp so mixture is heated under reflux to obtain a good yield of product
- Very slow reaction at Rtp so mixture is heated under reflux to obtain a good yield of product
- Halogen atom is replaced by an -OH group.
- Hydrolysis
- RATES of Hydrolysis
- The rate of hydrolysis depends
upon the strength of the
carbon-halogen bond in the
haloalkane
- As you go down the group of halides, the further down you go,
the weaker the bond between the halide and carbon. For
example// C-F is stronger than C-I as Iodine if further down the
group than flourine
- This means, the further down the group you go, the quicker the reaction as
not as much energy is required to break the bonds
- This means, the further down the group you go, the quicker the reaction as
not as much energy is required to break the bonds
- As you go down the group of halides, the further down you go,
the weaker the bond between the halide and carbon. For
example// C-F is stronger than C-I as Iodine if further down the
group than flourine
- Measuring the Rate of Hydrolysis of Primary Haloalkanes
- The rate of each reaction can be followed by carrying out the reaction in the presence of aqueous silver nitrate
- As the reaction occurs, halide ions that are produced (Cl-, Br-, I-) react with Ag+ ions
to form a precipitate of the silver halide
- Ag+ ion (aq) + X- ion (aq) --> AgX precipitate (s)
- A Haloalkane of 1-CHLORObutane forms a white precipitate very slowly
- A Haloalkane of 1-BROMObutane forms a cream precipitate at medium speed
- A Haloalkane of 1-IODObutane forms a yellow precipitate rapidly
- A Haloalkane of 1-CHLORObutane forms a white precipitate very slowly
- Ag+ ion (aq) + X- ion (aq) --> AgX precipitate (s)
- The nucleophile used is water, which is present in (aq) AgNO3. However
Haloalkanes are insoluble in water and the reaction is carried out in ethanol.
allowing water and the Haloalkanes to mix and produce a single solution
- As the reaction occurs, halide ions that are produced (Cl-, Br-, I-) react with Ag+ ions
to form a precipitate of the silver halide
- The rate of each reaction can be followed by carrying out the reaction in the presence of aqueous silver nitrate
- The rate of hydrolysis depends
upon the strength of the
carbon-halogen bond in the
haloalkane
- Hydrolysis of Primary, Secondary and Tertiary Haloalkanes
- Tertiary haloalkane hydrolyses fastest
- Two-Step Mechanism
- 1) Carbon-halogen bond of the tertiary haloalkane breaks by heterolyctic fission, forming a tertiary carbocation and a halide ion
- 2) A hydroxide ion attacks the carbocation to form the organic product
- 2) A hydroxide ion attacks the carbocation to form the organic product
- 1) Carbon-halogen bond of the tertiary haloalkane breaks by heterolyctic fission, forming a tertiary carbocation and a halide ion
- Two-Step Mechanism
- Primary haloalkane is hydrolysed slowest
- One-step Mechanism
- One-step Mechanism
- Tertiary haloalkane hydrolyses fastest
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