The correct structure of 1-bromo-2-methylbut-2ene is:

Options

A.
B.
C.
D.

Explanation

To determine the correct structure of 1-bromo-2-methylbut-2-ene, we can follow these steps:

### Step 1: Identify the Parent Chain
The name "but-2-ene" indicates that the parent chain consists of four carbon atoms (but-). The "2-ene" part tells us that there is a double bond between the second and third carbon atoms.

**Hint:** The prefix "but-" indicates a four-carbon chain.

### Step 2: Number the Carbon Atoms
We will number the carbon atoms in the chain starting from the end closest to the double bond to give the lowest possible numbers to the double bond. Thus, we will label the carbon atoms as follows:
- C1: First carbon
- C2: Second carbon (where the double bond starts)
- C3: Third carbon (where the double bond ends)
- C4: Fourth carbon

**Hint:** Number the chain to prioritize the double bond.

### Step 3: Add the Double Bond
According to the name "but-2-ene," we place a double bond between C2 and C3. The structure now looks like this:

```
C1 = C2 - C3 - C4
```

**Hint:** The double bond is between the second and third carbons.

### Step 4: Add the Methyl Group
The name "2-methyl" indicates that there is a methyl group (–CH3) attached to the second carbon. Therefore, we will add a methyl group to C2:

```
CH3
|
C1 = C2 - C3 - C4
```

**Hint:** The methyl group is attached to the second carbon.

### Step 5: Add the Bromine Atom
The "1-bromo" part of the name indicates that there is a bromine atom (Br) attached to the first carbon. So we will add a bromine atom to C1:

```
CH3
|
Br - C1 = C2 - C3 - C4
```

**Hint:** The bromine atom is attached to the first carbon.

### Step 6: Complete the Structure with Hydrogen Atoms
Now we will add hydrogen atoms to satisfy the tetravalency of carbon:
- C1 has one Br and one H (so it has 3 bonds)
- C2 has one double bond with C3, one bond with the methyl group, and one bond with H (so it has 4 bonds)
- C3 has one double bond with C2 and two H atoms (so it has 4 bonds)
- C4 has two H atoms and one bond with C3 (so it has 4 bonds)

The final structure will look like this:

```
CH3
|
Br - C1 = C2 - C3 - C4
| |
H H
```

### Final Structure
The complete structure of 1-bromo-2-methylbut-2-ene is:

```
CH3
|
Br - C1 = C2 - C3 - C4
| |
H H
```

### Conclusion
Thus, the correct structure of 1-bromo-2-methylbut-2-ene is drawn as above.

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