Basicity Of Pyridine Vs. Pyrrole

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Basicity of Pyridine vs Pyrrole

The lower the pKb value of a compound, the stronger a base it is. Since pyridine has a lower pKb value, it is a stronger base than pyrrole. In this example, we cannot use either the steric factor or inductive factor to explain their basicity. Instead, we have to look at the hybridization state of the respective nitrogen atoms.
The nitrogen atoms in pyrrole and pyridine are sp2 hybridized because they satisfy the following two conditions: 1) the atom has at least one lone pair of electrons and 2) the atom is connected to at least one sp2 hybridized atom.

An sp2 hybridized atom has three sp2 hybrid orbitals and 1 unhybridized p-orbital. A hybrid orbital is used to form a bond while an unhybridized p-orbital
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This explains why pyridine is a stronger base than pyrrole.

Example 1
Psilcoin is an active compound found in poisonous mushrooms and compound X is a derivative of Psilcoin.

Which of the following statement(s) about compound X is / are correct?
1. The nitrogen-containing group in the ring has a lower pKb value than the nitrogen-containing group in the side chain.
2. It reacts with both aqueous acids and alkalis.
3. It produces white fumes with ethanoyl chloride.
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Thus only NB atom can be protonated.

Gabriel Amine Synthesis (Preparation of 1o amines)
The Gabriel Amine synthesis is a three-step organic reaction that converts an alkyl halide to a primary amine. The advantage offered by Gabriel Amine synthesis is that it avoids poly-alkylation.

Step 1: acid-base reaction.
The acidic phthalimide molecule gets deprotonated by a strong base. The strength of an acid depends on the stability of the conjugate base. The negative charge on the conjugate base of phthalimide is delocalised over three highly electronegative oxygen and nitrogen atoms. The combined electron-withdrawing resonance and inductive effect ensures that the negative charge on the nitrogen atom is effectively dispersed.

Step 2: nucleophilic substitution
In Section 3.6 Halogen Derivatives, it was mentioned that an alkyl halide can undergo nucleophilic substitution by heating with excess alcoholic ammonia to yield a primary amine. Excess ammonia is necessary if a high yield of the primary amine is required. If excess ammonia is not used, poly-alkylation will occur as the amines are stronger nucleophiles than

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