Q57PE - Chemistry (OpenStax)

Question

Draw Lewis structures for pyridine and its conjugate acid, the pyridinium ion, \({C_5}{H_5}N{H^ + }.\) \(What are\) the geometries and hybridizations about the nitrogen atoms in pyridine and in the pyridinium ion?

Step-by-Step Solution

Answer

Hybridization and molecular geometry do not change when pyridine undergoes protonation and becomes a pyridinium ion.

Step 1: Pyridine

Pyridine is similar to the benzene ring - instead of one carbon atom in the structure, it has a nitrogen atom with its lone pair.

So, it's also aromatic and contains a \(\pi \) conjugated system of bonds inside the ring that have resonance structures.

Because of the conjugated \(\pi \) system and aromaticity, it has a planar structure.

         Pyridine

Step 2: Hybridisation of nitrogen in pyridine

The nitrogen atom here has 1 single bond, a double bond, and lone pair of electrons.

When it's present, in terms of determining hybridization, lone pair is considered a "single bond."

Therefore, if it has "2 single bonds" and one double bond.

We already know that when a double bond is present, it means that most likely \(s{p^2}\) hybridization is present

 

Step 3: The pyridinium ion

The pyridinium ion is slightly different than pyridine.

Here, the nitrogen atom is in its protonated form, which means it's positively charged.

Because of the conjugated \(\pi \) system and aromaticity, it has a planar structure.

      Pyridinium ion

Step 4: Hybridization of nitrogen in pyridinium ion

The nitrogen atom here has 2 single bonds and a double bond.

We already know that when a double bond is present, it means that most likely \(s{p^2}\) hybridization is present