Which of the following molecules represent the type of hybridization $sp^3, sp^2, sp^2$, sp from left to right atoms ?

Question

Accepted Answer

To determine the hybridization of each atom in the given molecules, we need to analyze the bonding and geometry around each atom. Let's examine each option to understand why Option 4 is correct and why the others are not.

### Option 4: $CH_3 - CH = CH - CN$

1. **First Atom ($CH_3$ group):**
   - The carbon in the $CH_3$ group is bonded to three hydrogen atoms and one carbon atom. This results in four sigma bonds, which corresponds to $sp^3$ hybridization.

2. **Second Atom ($CH$ group):**
   - The carbon in the $CH$ group is bonded to one hydrogen atom, one carbon atom with a double bond, and another carbon atom. This results in three sigma bonds and one pi bond, which corresponds to $sp^2$ hybridization.

3. **Third Atom ($CH$ group):**
   - The carbon in this $CH$ group is bonded to one hydrogen atom and has a double bond with the previous carbon and a single bond with the nitrogen in the CN group. This also results in three sigma bonds and one pi bond, corresponding to $sp^2$ hybridization.

4. **Fourth Atom (CN group):**
   - The carbon in the CN group is triple-bonded to nitrogen and single-bonded to the previous carbon. This results in two sigma bonds and two pi bonds, which corresponds to $sp$ hybridization.

Thus, Option 4 correctly represents the hybridization sequence $sp^3, sp^2, sp^2, sp$ from left to right.

### Explanation for Incorrect Options:

#### Option 1: $\ CH \equiv C - C \equiv CH$
- The first carbon is $sp$ hybridized due to the triple bond.
- The second carbon is $sp$ hybridized due to the triple bond.
- The third carbon is $sp$ hybridized due to the triple bond.
- The fourth carbon is $sp$ hybridized due to the triple bond.
- This sequence does not match $sp^3, sp^2, sp^2, sp$.

#### Option 2: $CH_2 = CH - C \equiv CH$
- The first carbon is $sp^2$ hybridized due to the double bond.
- The second carbon is $sp^2$ hybridized due to the double bond.
- The third carbon is $sp$ hybridized due to the triple bond.
- The fourth carbon is $sp$ hybridized due to the triple bond.
- This sequence does not match $sp^3, sp^2, sp^2, sp$.

#### Option 3: $CH_3 - CH = CH - CH_3$
- The first carbon is $sp^3$ hybridized due to four sigma bonds.
- The second carbon is $sp^2$ hybridized due to the double bond.
- The third carbon is $sp^2$ hybridized due to the double bond.
- The fourth carbon is $sp^3$ hybridized due to four sigma bonds.
- This sequence does not match $sp^3, sp^2, sp^2, sp$.

In conclusion, Option 4 is the only choice that correctly represents the hybridization sequence $sp^3, sp^2, sp^2, sp$ from left to right, making it the correct answer.