It is not always easy to predict the position of attack on multiply substituted benzene. If the benzene ring bears different group ortho/ para di- recting group at the 1 and 4 positions, the position of further substitution is not immediately clear.
Which of the following side chain reaction/s can be used to reduce the activity of strongly activat- ing groups like – OH

Options

A. benzoylation `(Ph-overset(O)overset("||")(C)-)`
B. acetylation `(CH_(3)-overset(O)overset("||")(C)-)`
C. both of the above
D. none of the above

Answer

To solve the problem regarding the reduction of the activity of strongly activating groups like –OH in a multiply substituted benzene, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Problem**: We have a benzene ring with a strongly activating group (–OH) at one position and a para-directing group at another position. The goal is to reduce the reactivity of the –OH group to achieve mono-substitution rather than tri-substitution.

2. **Understanding the Directing Effects**: The –OH group is an ortho/para-directing group, which means it increases the electron density at the ortho and para positions of the benzene ring. This increased electron density makes these positions more reactive towards electrophilic substitution.

3. **Protecting the –OH Group**: To reduce the reactivity of the –OH group, we can use protection strategies. This involves converting the –OH group into a less reactive substituent that does not direct electrophilic attack.

4. **Using Benzoylation**: One method to protect the –OH group is by benzoylation. In this reaction, the –OH group is converted into a benzoyloxy group (–OCOPh). This transformation reduces the availability of the lone pair on oxygen for resonance with the benzene ring, thus decreasing its activating effect.

5. **Using Acetylation**: Another method is acetylation, where the –OH group is converted into an acetoxy group (–OCOCH3). Similar to benzoylation, this reduces the electron-donating ability of the –OH group, making it less reactive in electrophilic aromatic substitution.

6. **Conducting the Electrophilic Substitution**: After protecting the –OH group, we can carry out the electrophilic substitution reaction (e.g., bromination) on the benzene ring. Since the –OH group is now less activating, we can achieve mono-substitution at the desired position.

7. **Final Product**: The final product will be a mono-substituted benzene derivative, where the original –OH group has been protected, allowing for controlled substitution.

### Conclusion:
By using benzoylation or acetylation to protect the –OH group, we can effectively reduce its reactivity and achieve mono-substitution on the benzene ring.