Benzene, Aromaticity and Electrophilic Substitution
Aromatic compounds satisfy Huckel's rule of 4n + 2 delocalised π electrons in a planar cyclic system and react by electrophilic substitution.
What is Benzene, Aromaticity and Electrophilic Substitution?
Aromatic compounds satisfy Huckel's rule of 4n + 2 delocalised π electrons in a planar cyclic system and react by electrophilic substitution.
Key formula / rule: Huckel's rule requires a planar cyclic conjugated system with 4n + 2 π electrons.
Key points
- Evaluate whether a ring system is aromatic using Huckel's rule.
- Predict the directing effect of a substituent on electrophilic substitution.
Common exam trap
Predicting addition rather than substitution for benzene.
Definitions
- Term
Benzene, Aromaticity and Electrophilic Substitution
- Meaning
Aromatic compounds satisfy Huckel's rule of 4n + 2 delocalised π electrons in a planar cyclic system and react by electrophilic substitution.
- Term
Benzene, Aromaticity and Electrophilic Substitution — explanation
- Meaning
Substitution preserves the aromatic sextet, which is why benzene substitutes rather than adds. Existing substituents direct incoming groups by their electronic effect.
Learning objectives
Evaluate whether a ring system is aromatic using Huckel's rule.
Predict the directing effect of a substituent on electrophilic substitution.
Formulae
- Key point
Huckel's rule requires a planar cyclic conjugated system with 4n + 2 π electrons.
- Key point
Activating groups direct ortho and para; deactivating groups other than halogens direct meta.
- Key point
Halogens are deactivating yet ortho-para directing.
Prerequisites
CHE-U4-HC-T1-S1-C2
Common mistakes
Predicting addition rather than substitution for benzene.
Assigning halogens as meta directors because they deactivate.
Keywords
Benzene
Aromaticity
Electrophilic
Substitution
Practice preview
Which of the following rules is primarily used to determine the aromaticity of a cyclic, planar compound?…
easy
What is the hybridisation of each carbon atom in the benzene ring?…
easy
Which of the following reagents is typically used for the nitration of benzene?…
easy