Organic Chemistry Terminology (Cambridge (CIE) A Level Chemistry)
Revision Note
Organic Chemistry Terminology
Organic reactions are often associated with terminology students should be familiar with
Two of these important terms include:
Electrophilic substitution
Addition-elimination
Electrophilic substitution
Electrophiles are species that are electron deficient and can act as an electron pair acceptor
Electrophiles are ‘electron loving’ species
Substitution reactions are reactions that involve the replacement of one atom or group of atoms by another
Electrophilic substitution reactions are therefore reactions in which an atom or group of atoms are replaced by an electrophile after an initial attack by the electron-deficient species
An example of an electrophilic substitution reaction is the reaction of benzene with bromine in the presence of anhydrous aluminium bromide catalysts
The bromine acts as an electrophile and attacks the electron-rich benzene ring
A hydrogen atom is substituted by a bromine atom to form bromobenzene and hydrogen bromide
Benzene undergoes substitution reactions rather than addition reactions because of the stability of the benzene ring
Electrophilic substitution of benzene by bromine
A hydrogen atom in benzene is substituted by a bromine atom, which acts as an electrophile
Addition-elimination
Acyl chlorides are reactive organic compounds that undergo many reactions such as nucleophilic addition-elimination reactions
In nucleophilic addition-elimination reactions, the nucleophilic addition of a small molecule across the C=O bond takes place followed by elimination of a small molecule
Examples of these nucleophilic addition-elimination reactions include:
Hydrolysis
Reaction with alcohols to form esters
Reaction with ammonia and primary amines to form amides
Hydrolysis
The hydrolysis of acyl chlorides results in the formation of a carboxylic acid and HCl molecule
This is a nucleophilic addition-elimination reaction
A water molecule adds across the C=O bond
A hydrochloric acid (HCl) molecule is eliminated
Hydrolysis of propanoyl chloride to form propanoic acid and HCl
Acyl chlorides are hydrolysed to carboxylic acids via nucleophilic addition-elimination
Formation of esters
Acyl chlorides can react with alcohols to form esters
The esterification of acyl chlorides is also a nucleophilic addition-elimination reaction
The alcohol adds across the C=O bond
A HCl molecule is eliminated
Esterification of propanoyl chloride to form ethyl propanoate and HCl
Acyl chlorides are esterified with alcohols to form esters via nucleophilic addition-elimination
Formation of amides
Acyl chlorides can form amides with primary amines and concentrated ammonia
The nitrogen atom in ammonia and primary amine has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides
The product is an amide (when reacted with ammonia) or N-substituted amide (when reacted with primary amines)
This is also an example of a nucleophilic addition-elimination reaction as
The amine or ammonia molecule adds across the C=O bond
A HCl molecule is eliminated
Forming amides from propanoyl chloride
Acyl chlorides undergo reactions with ammonia and primary amines to form amides via nucleophilic addition-elimination
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