Which ester on pyrolysis gives isobutylene -

Options

A. `CH_(3)-CH_(2)-CH_(2)-O-underset(O)underset(||)(C)-CH_(3)`
B. `CH_(3)COOCH_(2)CH_(2)CH_(3)`
C. `CH_(3)COOCH_(2)-CH(CH_(3))_(2)`
D. All the above

Answer

To determine which ester gives isobutylene upon pyrolysis, we need to understand the process of pyrolysis and the structure of the esters involved. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Pyrolysis
In pyrolysis, an ester undergoes thermal decomposition to yield an alkene and a carboxylic acid. The reaction involves the breaking of bonds and the formation of new ones.

**Hint:** Pyrolysis involves breaking down an ester into an alkene and a carboxylic acid.

### Step 2: Identify the Structure of Esters
We need to analyze the structures of the given esters. The general structure of an ester is RCOOR', where R and R' are hydrocarbon chains.

**Hint:** Look for the ester functional group (–COOR) in the options provided.

### Step 3: Analyze the Given Options
Let’s evaluate the options one by one to see which one can produce isobutylene (2-methylpropene).

1. **Option 1:** CH3COO(CH2)2CH3
2. **Option 2:** CH3COO(CH2)2CH2CH3
3. **Option 3:** CH3COO(CH2)C(CH3)2

**Hint:** Focus on the branching of the carbon chains and the position of the functional groups.

### Step 4: Perform Elimination Reaction
For each ester, we will perform the elimination reaction to see if isobutylene can be formed.

- **Option 1:** The elimination would not yield isobutylene as it does not have the required branching.

- **Option 2:** Similar to option 1, it lacks the necessary structure to form isobutylene.

- **Option 3:** Here, we have CH3COO(CH2)C(CH3)2. The carbon adjacent to the ester (alpha carbon) can lose a hydrogen atom, while the carbon with the methyl group (beta carbon) can lose the ester group. This will lead to the formation of a double bond between the alpha and beta carbons.

**Hint:** Look for the possibility of forming a double bond between the alpha and beta carbons during elimination.

### Step 5: Confirm the Formation of Isobutylene
In option 3, after the elimination, we can see that the structure formed is 2-methylpropene (isobutylene), which has the following structure:

- The double bond is formed between the second and third carbon atoms, resulting in the structure CH2=C(CH3)2.

**Hint:** Isobutylene has a specific structure (2-methylpropene) that you can recognize.

### Conclusion
After analyzing all the options, we conclude that **Option 3** (CH3COO(CH2)C(CH3)2) is the ester that gives isobutylene upon pyrolysis.

**Final Answer:** Option 3 gives isobutylene upon pyrolysis.