If the dipole moment of Toluene and Nitro - benzene are 0.43 D and 3.93 D respectively, then what is the expected dipole moment of p-Nitrotoluene?

Options

A. 3.50 D
B. 2.18 D
C. 4.36 D
D. 5.30 D

Answer

To find the expected dipole moment of p-Nitrotoluene, we will follow these steps:

### Step 1: Understand the Structure
- **Toluene** has a methyl group (CH3) attached to a benzene ring, while **Nitrobenzene** has a nitro group (NO2) attached to a benzene ring. In p-Nitrotoluene, both the methyl and nitro groups are attached to the benzene ring at the para positions.

### Step 2: Identify the Dipole Moments
- The dipole moment of **Toluene** is given as **0.43 D** (Debye).
- The dipole moment of **Nitrobenzene** is given as **3.93 D** (Debye).

### Step 3: Determine the Direction of Dipole Moments
- The methyl group (CH3) is an electron-donating group, which means it has a positive inductive effect (+I). Therefore, the dipole moment due to the methyl group points towards the benzene ring.
- The nitro group (NO2) is an electron-withdrawing group, which means it has a negative inductive effect (-I). Thus, the dipole moment due to the nitro group points towards the nitro group itself.

### Step 4: Combine the Dipole Moments
- Since the dipole moments of the methyl group and the nitro group are in opposite directions, we can add their magnitudes to find the resultant dipole moment of p-Nitrotoluene.

\[ \text{Dipole moment of p-Nitrotoluene} = \text{Dipole moment of Toluene} + \text{Dipole moment of Nitrobenzene} \]
\[ = 0.43 \, \text{D} + 3.93 \, \text{D} = 4.36 \, \text{D} \]

### Step 5: Conclusion
- The expected dipole moment of p-Nitrotoluene is **4.36 D**.