Q.Number of π bonds and σ bonds in the following structure is—

The key idea for solving this problem is Sigma Pi Bond Counting. We need to systematically count the number of $\sigma$ (sigma) and $\pi$ (pi) bonds in the given structure, naphthalene.

Here's the essential reasoning:

1. Count $\pi$ bonds: Naphthalene (C$_{10}$H$_8$) consists of two fused benzene rings. The structure contains 5 double bonds. Each double bond contributes one $\pi$ bond. Therefore, the number of $\pi$ bonds is 5.

2. Count $\sigma$ bonds:

   • C-H $\sigma$ bonds: Naphthalene has 8 hydrogen atoms, each forming a single bond with a carbon atom. Thus, there are 8 C-H $\sigma$ bonds.
   • C-C $\sigma$ bonds: We can use a general formula for $\sigma$ bonds in a polycyclic hydrocarbon: $N_{\sigma} = C + H + R - 1$, where $C$ is the number of carbon atoms, $H$ is the number of hydrogen atoms, and $R$ is the number of rings. For naphthalene, $C=10$, $H=8$, and $R=2$ (two fused rings). So, $N_{\sigma} = 10 + 8 + 2 - 1 = 19$.

   Alternatively, by direct counting: …

Understanding the nature of chemical bonds is fundamental to organic chemistry. Sigma ($\sigma$) and pi ($\pi$) bonds are the two main types of covalent bonds formed between atoms.

• Sigma ($\sigma$) bonds: These are formed by the direct, head-on overlap of atomic orbitals (s-s, s-p, or p-p axial overlap). They are the strongest type of covalent bond and are present in all single, double, and triple bonds. A single bond always consists of one $\sigma$ bond.
• Pi ($\pi$) bonds: These are formed by the sideways overlap of unhybridized p-orbitals. They are weaker than $\sigma$ bonds and are found in double and triple bonds. A double bond consists of one $\sigma$ bond and one $\pi$ bond. A triple bond consists of one $\sigma$ bond and two $\pi$ bonds.

To count the $\sigma$ and $\pi$ bonds in a molecule, we first need its correct structural representation, showing all atoms and bonds.

1. Draw the structure of Naphthalene (C$_{10}$H$_8$).

   Naphthalene consists of two fused benzene rings. It has 10 carbon atoms and 8 hydrogen atoms. The two rings share two carbon atoms. Each of the other 8 carbon atoms is bonded to one hydrogen atom. A common Kekulé structure for naphthalene is shown below:

   

   (Note: The lines represent bonds. Double lines represent double bonds, single lines represent single bonds.)

2. Count the $\pi$ bonds.

   Each double bond contains one $\pi$ bond. By examining the Kekulé structure above, we can count the double bonds:

   • There are 5 double bonds in the naphthalene structure.
   • Each of these 5 double bonds contributes one $\pi$ bond.

   Therefore, the number of $\pi$ bonds is 5.

3. Count the $\sigma$ bonds.

   Each single bond is a $\sigma$ bond, and each double bond also contains one $\sigma$ bond. We can count $\sigma$ bonds by categorizing them into C-H bonds and C-C bonds.

   • Count C-H $\sigma$ bonds:

     Naphthalene has the formula C$_{10}$H$_8$. This means there are 8 hydrogen atoms, and each is bonded to a carbon atom by a single bond.

     Number of C-H $\sigma$ bonds = 8.

   • Count C-C $\sigma$ bonds:

     The skeletal structure of naphthalene consists of 10 carbon atoms forming two fused rings. …