Addition of one equivalent of bromine to 1, 3-pentadiene produces

Options

A. 1, 5-Dibromo-2-pentene
B. 4, 5-dibromo-2-pentene
C. 3, 4-dibromopentene
D. 3, 4-dibromo-2-pentene

Answer

To solve the problem of what product is formed when one equivalent of bromine is added to 1,3-pentadiene, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure of 1,3-Pentadiene**:
- 1,3-Pentadiene has the formula C5H8 and contains two double bonds located at the first and third carbon atoms. Its structure can be represented as:
\[ \text{CH}_2=CH-CH=CH-CH_3 \]

2. **Addition of Bromine**:
- When bromine (Br2) is added to 1,3-pentadiene, it undergoes an electrophilic addition reaction. The double bond acts as a nucleophile and attacks one of the bromine atoms, leading to the formation of a bromonium ion.

3. **Formation of Bromonium Ion**:
- The addition of bromine results in the formation of a bromonium ion intermediate. The structure of the bromonium ion can be represented as:
\[ \text{CH}_2Br^+-CH-CH=CH-CH_3 \]
- This intermediate is stabilized by resonance.

4. **Formation of Products**:
- The bromonium ion can lead to two possible products due to the rearrangement of the positive charge (carbocation) and the attack of the bromide ion (Br-) on different carbon atoms. The two main products are:
- **Product 1**: From the attack of Br- at the second carbon:
\[ \text{CH}_2Br-CHBr-CH=CH-CH_3 \]
- **Product 2**: From the attack of Br- at the fourth carbon:
\[ \text{CH}_2Br-CH-CHBr-CH_3 \]

5. **Naming the Products**:
- The first product can be named as 4,5-dibromo-1-pentene, while the second product can be named as 3,4-dibromo-1-pentene. However, the product that is formed predominantly is 4,5-dibromo-1-pentene.

6. **Final Answer**:
- Therefore, the addition of one equivalent of bromine to 1,3-pentadiene produces **4,5-dibromo-1-pentene**.