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 para-nitrotoluene, we will use the dipole moments of toluene and nitrobenzene. Here’s a step-by-step solution:

### Step 1: Understand the Dipole Moments
- The dipole moment of toluene (C7H8) is given as **0.43 D**.
- The dipole moment of nitrobenzene (C6H5NO2) is given as **3.93 D**.

### Step 2: Analyze the Structure of para-Nitrotoluene
- In para-nitrotoluene, the nitro group (NO2) is located at the para position relative to the methyl group (CH3) on the benzene ring.
- The methyl group is an electron-donating group, which contributes to a positive dipole moment.
- The nitro group is an electron-withdrawing group, contributing to a negative dipole moment.

### Step 3: Determine the Direction of Dipole Moments
- The dipole moment due to the methyl group points towards the methyl group (from the benzene ring to the methyl group).
- The dipole moment due to the nitro group points towards the nitro group (from the benzene ring to the nitro group).
- Since both dipole moments are aligned in the same direction (towards the nitro group), we can add them together.

### Step 4: Calculate the Total Dipole Moment
- The total dipole moment of para-nitrotoluene can be calculated by adding the dipole moments of toluene and nitrobenzene:
\[ \text{Dipole moment of para-nitrotoluene} = \text{Dipole moment of toluene} + \text{Dipole moment of nitrobenzene} \]
\[ = 0.43 \, D + 3.93 \, D = 4.36 \, D \]

### Step 5: Conclusion
- Therefore, the expected dipole moment of para-nitrotoluene is **4.36 D**.