Reactions of Arenes. Electrophilic Aromatic Substitution
Electrophilic Aromatic Substitution of Heteroaromatics
Aromatic compounds which contain heteroatoms (e.g. O, N,
S) are called heteroaromatics.
The presence of the heteroatom influences the reactivity compared to benzene.
The 5-membered ring heterocycles (furan, pyrrole, thiophene)
are p-electron richaromatics
(6p electrons over 5 atoms)
This makes them more reactive than benzene (since the aromatics the nucleophilic
component in these electrophilic substitution reactions)
For example furan is similar to an activated benzene like methoxybenzene
Pyridine is less reactive than benzene (more like nitrobenzene)
due to the electronegativity of N, it is described as a p-electron
defficientaromatic
The basic nature of the N atom of pyridine often interferes and interacts
with the electrophile E+ which further
deactivates the system
Compound Name
Line Drawing
3D Model
Furan
Thiophene
Pyrrole
Pyridine
The 5 membered heterocycles react in a similar way. As an example here
is the general pattern for the electrophilic aromatic substitution reactivity
of furan, complete with the 3 important resonance structures that justify
the reactivity of the 2-position.
How many important resonance structures can you draw for reaction at
the 3-position ?
