Question

compare activity of pyridine, pyrimidine,pyrrole and benzene in the electrophilic substitution reactions.explain your schemes of their nomination reactions.

Answer 1

Pyridine is the most reactive in electrophilic substitution reactions, followed by pyrimidine and pyrrole. Benzene is the least reactive due to its stable aromatic system. The reactivity of these compounds is based on the presence and location of electron-donating or electron-withdrawing groups in the ring.

Step-by-step explanation:

Pyridine, pyrimidine, pyrrole, and benzene can all undergo electrophilic substitution reactions, but their reactivity and the products formed can vary.

Pyridine:

Pyridine is the most reactive of the four compounds due to the presence of a nitrogen atom in the ring, which can donate electrons to stabilize positive charges. It undergoes electrophilic substitution reactions more readily than benzene or the other compounds.

Pyrimidine:

Pyrimidine is less reactive than pyridine but more reactive than benzene. It can undergo electrophilic substitution reactions, but the nitrogen atoms in the ring are not as effective at stabilizing positive charges as in pyridine.

Pyrrole:

Pyrrole is less reactive than both pyridine and pyrimidine due to the presence of a lone pair of electrons on the nitrogen atom. This lone pair forms a resonance structure with the π-electron system, reducing the electron density at the carbon atoms and making it less susceptible to electrophilic attack.

Benzene:

Benzene is the least reactive of the four compounds due to its stable aromatic system. It requires stronger electrophiles than an alkene to react and follows a different reaction route than an alkene. Benzene undergoes electrophilic aromatic substitution reactions, such as halogenation, nitration, sulfonation, alkylation, and acylation.

Answer 2

Benzene undergoes electrophilic aromatic substitution but requires strong electrophiles due to its weak nucleophilicity. Pyrrole is more reactive, while pyridine and pyrimidine are less reactive, with the latter being the least due to its electron-deficient nature.

Step-by-step explanation:

When comparing the activity of pyridine, pyrimidine, pyrrole, and benzene in electrophilic substitution reactions, it's important to consider their electronic structures and the impact these have on their reactivity. Benzene, with its delocalized π-electrons, undergoes electrophilic aromatic substitution reactions where an electrophile replaces a hydrogen atom. However, the nucleophilic character of benzene is relatively weak due to aromatic stabilization, meaning it requires stronger electrophiles for reaction. In contrast, pyrrole is more reactive towards electrophilic substitution due to the lone pair on the nitrogen being part of the aromatic π-system, increasing electron density and its nucleophilicity. Pyridine is less reactive towards such reactions since the lone pair on nitrogen is not part of the aromatic π-system, making it less nucleophilic. Pyrimidine is even less reactive because of its electron-deficient nature, making it less likely to participate in these reactions without strong activation conditions.