Which of the following compound will undergo tautomerism?

Options

A.
B.
C.
D.

Answer

To determine which compound undergoes tautomerism, we need to follow these steps:

### Step 1: Understand Tautomerism
Tautomerism is a type of isomerism where structural isomers (tautomers) readily interconvert, typically involving the relocation of a proton (H+) and a shift in the position of a double bond. For tautomerism to occur, the compound must have an alpha hydrogen (a hydrogen atom attached to the carbon adjacent to a functional group).

**Hint:** Look for the presence of alpha hydrogens in the compounds given.

### Step 2: Analyze the First Compound
Examine the first compound structure. Identify the alpha carbon and check for the presence of alpha hydrogens.

- If there are alpha hydrogens, consider how they can shift to form a new structure.
- If the resulting structure leads to a situation where double bonds are directly connected, it indicates tautomerism cannot occur.

**Hint:** Identify the alpha hydrogen and visualize the proton transfer and double bond shift.

### Step 3: Analyze the Second Compound
Look at the second compound, which has a benzene ring with two methyl groups on the alpha carbon.

- Check the alpha carbon for alpha hydrogens.
- If all substituents on the alpha carbon are groups (like methyl), then there are no alpha hydrogens present.

**Hint:** Remember that the presence of substituents can block the possibility of tautomerism.

### Step 4: Analyze the Third Compound
Examine the third compound, which is benzaldehyde (a benzene ring with an aldehyde group).

- Identify the alpha carbon and check for alpha hydrogens.
- If there are no alpha hydrogens present on the alpha carbon, tautomerism cannot occur.

**Hint:** Look for the aldehyde group and its effect on the alpha hydrogen availability.

### Step 5: Analyze the Fourth Compound
Now consider the fourth compound, which is a simple ketone or aldehyde structure.

- Identify the alpha carbon and check for the presence of alpha hydrogens.
- If there are alpha hydrogens present, tautomerism can occur.

**Hint:** Ensure to visualize the proton transfer and double bond shift to confirm tautomerism.

### Conclusion
After analyzing all the compounds:
- The first, second, and third compounds do not have alpha hydrogens, thus they cannot undergo tautomerism.
- The fourth compound has alpha hydrogens, allowing it to undergo tautomerism.

**Final Answer:** The compound that will undergo tautomerism is the fourth one.