Haloalkanes Flashcards
Why are haloalkanes more reactive than alkanes?
Haloalkanes are much more reactive than alkanes due to the presence of the electronegative halogens
Is the C-X bond polar?
Due to the large difference in electronegativity between the carbon and halogen atom, the C-X bond is polar
What happens during a nucleophilic substitution reaction?
A halogen is substituted for another atom or group of atoms
What are the products formed from nucleophilic substitutions?
The products formed when haloalkanes undergo this type of reaction are alcohols, amines and nitriles
What happens during an elimination reaction?
A hydrogen halide is eliminated during the reaction
What are the products formed from eliminations?
The key product formed from this type of reaction is an alkene
What solution is used for the formation of alcohols from halogenoalkanes?
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
How do we combine the two solutions (the NaOH/KOH) - an aqueous solution with the halogenoalkane, an organic solution?
The use of ethanol allows the aqueous sodium hydroxide layer and the organic halogenoalkane layer to mix, allowing the reaction to proceed
The reaction between the halogenoalkane and the nucleophile is very slow. How do we speed it up?
This reaction is very slow at room temperature, so the reaction mixture is warmed
What other aspects does rate of reaction rely on in the formation of alcohols?
The rate of this reaction depends on the type of halogen in the haloalkanes
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
For example, fluoroalkanes do not react at all, but iodoalkanes have a very fast rate of reaction
What is a nucelophile?
A 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
What is a nucleophilic substitution reaction?
A nucleophilic substitution reaction is one in which a nucleophile attacks a carbon atom which carries a partial positive charge
Why do halogenoalkanes undergo nucleophilic substitution reactions?
Haloalkanes will undergo nucleophilic substitution reactions due to the polar C-X bond (where X is a halogen)
