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Chemistry Question 66 – NEET-UG 2023

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The number of σ bonds, π bonds and lone pair of electrons in pyridine, respectively are:

To determine the number of σ bonds, π bonds, and lone pairs, it is essential to first draw the correct Lewis structure of the molecule.

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Ninja Strategy•Lone Pair and Pi Bond Count

Quickly identify that pyridine has 3 pi bonds (due to aromaticity) and 1 lone pair on the nitrogen atom. This immediately eliminates options that state 0 lone pairs or 2 pi bonds.

Step 1: Draw the structure of Pyridine✦ Active

Pyridine (C5H5N) is a six-membered heterocyclic aromatic ring. The ring consists of five carbon atoms and one nitrogen atom. Each carbon atom is bonded to one hydrogen atom. The nitrogen atom has one lone pair of electrons. The structure contains three double bonds within the ring.

💡 Teacher's Secret Hint

Remember that pyridine is an analogue of benzene where one CH group is replaced by N.

Step 2: Count the σ bonds○ Expand

In the pyridine ring, there are 6 sigma bonds forming the cyclic structure (5 C-C sigma bonds and 1 C-N sigma bond, or 4 C-C and 2 C-N depending on the specific bond types, but total 6 connections in the ring). Additionally, each of the 5 carbon atoms is bonded to one hydrogen atom, contributing 5 C-H sigma bonds. Therefore, the total number of σ bonds is 6 (ring)+5 (C-H)=11.

💡 Teacher's Secret Hint

Each single bond is a σ bond, and each double bond contains one σ bond.

Step 3: Count the π bonds and lone pairs○ Expand

Pyridine is an aromatic compound with three double bonds in the ring. Each double bond contributes one π bond. So, the total number of π bonds is 3. The nitrogen atom in pyridine has one lone pair of electrons, which resides in an sp2 orbital and is not part of the aromatic π system. Thus, there is 1 lone pair of electrons. Therefore, the number of σ bonds, π bonds, and lone pair of electrons are 11, 3, and 1, respectively.

💡 Teacher's Secret Hint

The lone pair on nitrogen in pyridine is not involved in aromaticity, unlike in pyrrole.

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