Question 55: The number of \sigma bonds, \pi bonds and lone pair of electrons in pyridine, respectively are:
(1) 11,3,1
(2) 12,2,1
(3) 11,2,0
(4) 12,3,0
Answer: Option (1)
Explanation:
Pyridine is a six-membered aromatic ring containing five carbon atoms and one nitrogen atom.
In the ring, there are six single bonds between adjacent atoms, and each single bond represents one \sigma bond. Thus, the ring contributes 6 \sigma bonds.
There are five \mathrm{C–H} bonds in pyridine, and each \mathrm{C–H} bond is a \sigma bond. Hence, these contribute 5 more \sigma bonds.
Therefore, total number of \sigma bonds is:
6 + 5 = 11Pyridine is aromatic and contains three alternating double bonds in the ring. Each double bond has one \pi bond.
Hence, the number of \pi bonds is 3.
The nitrogen atom in pyridine has one lone pair of electrons, which is not involved in aromaticity.
Thus, the numbers of \sigma bonds,
\pi bonds, and lone pairs are 11, 3, 1, respectively.
Therefore, the correct option is Option (1).