The IUPAC name of the compound shown below is?
`Cl -CH=CH_2 - CH_2 - CH_2 Br`

Options

A. 1-chloro-4-bromo but-1-ene
B. 4-chloro-1-bromo but-3-ene
C. 4-bromo-1-chloro but-1-ene
D. 1-bromo-4-chloro but-3-ene

Explanation

To determine the IUPAC name of the compound `Cl -CH=CH2 - CH2 - CH2 Br`, we can follow these steps:

### Step 1: Identify the longest carbon chain
The compound has a total of 5 carbon atoms in the longest continuous chain. The structure can be represented as:
```
Cl - C1 = C2 - C3 - C4 - C5 - Br
```
This indicates that the longest chain is a 5-carbon chain.

**Hint:** Look for the longest continuous chain of carbon atoms to establish the parent hydrocarbon.

### Step 2: Number the carbon chain
We need to number the carbon chain in such a way that the double bond gets the lowest possible number. Starting from the end closest to the double bond:
```
1. Cl - C1 = C2 - C3 - C4 - C5 - Br
```
If we number from left to right:
- C1 has Cl (Chloro)
- C2 has the double bond
- C4 has Br (Bromo)

So, the numbering is:
1. C1 (Cl)
2. C2 (double bond)
3. C3
4. C4 (Br)
5. C5

**Hint:** Always number the chain from the end that gives the double bond the lowest number.

### Step 3: Identify substituents and their positions
From our numbering:
- The chlorine (Cl) is on carbon 1 (1-Chloro).
- The bromine (Br) is on carbon 4 (4-Bromo).

**Hint:** Identify and note the positions of all substituents on the carbon chain.

### Step 4: Determine the root name and the type of bond
The longest chain has 5 carbon atoms, which corresponds to "pentane". Since there is a double bond, we change "pentane" to "pentene". The position of the double bond is at carbon 2, so we have "pent-2-ene".

**Hint:** The suffix for alkenes is "-ene", and the position of the double bond is indicated by the lowest numbered carbon involved in the double bond.

### Step 5: Combine the substituents and the root name
When combining the substituents with the root name, we list them in alphabetical order:
- Bromo comes before Chloro in alphabetical order.

Thus, the complete IUPAC name is:
**4-Bromo-1-chloropent-2-ene**

### Final Answer
The IUPAC name of the compound `Cl -CH=CH2 - CH2 - CH2 Br` is **4-Bromo-1-chloropent-2-ene**.