Write down the products of ozonolysis of 1, 2-dimethylbenzene (o-xylene). How does the result support Kekulé structure for benzene?

Explanation

To solve the problem of determining the products of ozonolysis of 1,2-dimethylbenzene (o-xylene) and how the result supports the Kekulé structure for benzene, we can follow these steps:

### Step 1: Understand the Structure of o-Xylene
1,2-Dimethylbenzene, commonly known as o-xylene, has a benzene ring with two methyl groups attached to adjacent carbon atoms (the ortho position). The structure can be represented as follows:

```
CH3
|
C6H4 - C
|
CH3
```

### Step 2: Ozonolysis Reaction
Ozonolysis involves the reaction of an alkene with ozone (O3), followed by reduction. In the case of o-xylene, the double bonds in the benzene ring are not directly involved in ozonolysis; instead, the reaction will cleave the carbon-carbon bonds adjacent to the methyl groups.

### Step 3: Predict the Products
When o-xylene undergoes ozonolysis, the following products are formed:
1. **Methylglyoxal (CH3C(=O)CHO)**: This compound results from the cleavage of the carbon-carbon bond between one of the methyl groups and the adjacent carbon in the benzene ring.
2. **Glyoxal (C2H2O2 or O=CH-CHO)**: This compound is formed from the cleavage of the carbon-carbon bond adjacent to the other methyl group.

Thus, the products of ozonolysis of o-xylene are:
- Methylglyoxal (CH3C(=O)CHO)
- Glyoxal (O=CH-CHO)

### Step 4: Analyze the Resonance Structures
The presence of two distinct products (methylglyoxal and glyoxal) indicates that the structure of o-xylene is not fixed but rather a resonance hybrid of two structures. The two resonance structures can be drawn as follows:

1. **Resonance Structure 1**:
- Methyl groups at positions 1 and 2 with alternating double bonds.

2. **Resonance Structure 2**:
- Methyl groups at positions 1 and 2 with the double bonds shifted.

### Step 5: Conclusion on Kekulé Structure
The formation of two different products from the ozonolysis of o-xylene supports the idea that the benzene ring can be represented as a resonance hybrid of multiple structures (Kekulé structures). If benzene were to have a fixed structure, we would expect only one product from the ozonolysis. However, the presence of multiple products indicates that the actual structure of benzene is a hybrid of these resonance forms, thus supporting Kekulé's model.

### Summary of Products
- Methylglyoxal (CH3C(=O)CHO)
- Glyoxal (O=CH-CHO)