It is not always easy to predict the position of attack on multiply substituted benzene. If the benzene ring bears different ortho//para directing group at the `1` and `4` positions, the position of further substitution is not immediately clear. Sometimes steric effects determine the outcome. In other cases, electronic factors determine the outcome, and further reaction will be at the position activated by the more strongly activating group.
Some substituens are so strongly activating that no catalyst is needed, and it is often diffcult to stop substitution after mono substituion. Mild condition are needed to restrict the reaction to mono-substitution.
It is possible to reduce the activity such groups by side chain reaction so that the reaction can be stopped use can sometimes be made of removable blocking groups on the ring.
Which of the following synthesis could be done in the ring step ?

Options

A.
B.
C.
D.

Answer

To solve the problem of predicting the position of attack on multiply substituted benzene, we need to analyze the substituents on the benzene ring and their effects on electrophilic substitution reactions. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Substituents
First, we need to identify the substituents on the benzene ring in the given compounds. We must note whether they are activating or deactivating groups and whether they direct substitution to the ortho or para positions.

**Hint:** Look for groups that are electron-donating (activating) or electron-withdrawing (deactivating) to determine their influence on the benzene ring.

### Step 2: Determine the Directing Effects
Next, we analyze the directing effects of the substituents. Activating groups generally direct electrophilic substitution to the ortho and para positions, while deactivating groups direct it to the meta position. In this case, all substituents are activating groups.

**Hint:** Remember that ortho and para positions are favored for activating groups, while meta positions are favored for deactivating groups.

### Step 3: Assess Steric Hindrance
For the compounds that are disubstituted, we need to consider steric hindrance. If there is a substituent at the para position that is bulky, it can block further substitution at that position.

**Hint:** Check if any substituent at the para position is bulky enough to hinder the approach of the electrophile.

### Step 4: Evaluate Each Compound
Now, we evaluate each compound:
- **Compound A, B, and D:** All have a substituent at the para position that is bulky (like a methyl group), which blocks substitution at that position. Therefore, bromination cannot occur at the para position.
- **Compound C:** The para position is open, allowing for bromination to occur at either the ortho or para position without steric hindrance.

**Hint:** Compare the positions of substituents in each compound to see which positions are blocked and which are open for substitution.

### Step 5: Conclusion
Based on the analysis, only Compound C allows for bromination to occur in a single step because both ortho and para positions are available for electrophilic attack. The other compounds cannot undergo substitution at the para position due to steric hindrance.

**Final Answer:** The synthesis that could be done in a single step is **Option C**, where phenol can be converted into ortho-bromo phenol.