Which of the following is correct IUPAC name ?

Options

A. `2`-Bromo cyclohex-`5`-ene carbaldehyde
B. Ethyl-`2`-vinyl pentanoate
C. `5`-Bromo-`3`-chlorohept-`3`-ene
D. `2`-Ethenylhexa-`1,5`-diene

Answer

To determine which of the given options has the correct IUPAC name, we will analyze each option step by step.

### Step 1: Analyze Option A - 2-bromocyclohexene-1-carbaldehyde
1. **Identify the structure**: The name suggests a cyclohexene ring with a bromine substituent and a carbaldehyde group (CHO).
2. **Draw the structure**:
- Cyclohexene has 6 carbon atoms in a ring with a double bond.
- The carbaldehyde group (CHO) has the highest priority and should be at position 1.
- The bromine should be at position 2.
3. **Numbering**: Start numbering from the carbon of the aldehyde (CHO) as position 1.
- This gives us: 1 (CHO), 2 (Br), 3, 4, 5, 6.
4. **Correct IUPAC name**: The correct name should be 6-bromo-2-cyclohexene-1-carbaldehyde, not 2-bromocyclohexene-1-carbaldehyde. Thus, Option A is incorrect.

### Step 2: Analyze Option B - Ethyl 2-vinylpentanoate
1. **Identify the structure**: This suggests a pentanoate (5 carbon chain) with an ethyl and a vinyl group.
2. **Draw the structure**:
- Pentanoate means a 5-carbon chain with an ester functional group.
- Ethyl group (C2H5) and vinyl group (C=C) need to be positioned.
3. **Numbering**: The vinyl group cannot act as a substituent; it must be part of the main chain. Thus, the numbering should start from the carboxylic acid end.
4. **Correct IUPAC name**: The correct name should be ethyl 3-vinylbutanoate. Therefore, Option B is incorrect.

### Step 3: Analyze Option C - 5-bromo-3-chlorohept-3-ene
1. **Identify the structure**: This suggests a heptene (7 carbon chain) with bromine and chlorine substituents.
2. **Draw the structure**:
- Hept-3-ene indicates a double bond between carbons 3 and 4.
- Bromine at position 5 and chlorine at position 3.
3. **Numbering**: Start numbering from the end closest to the double bond to give the lowest possible numbers to the substituents.
- This gives us: 1, 2, 3 (Cl), 4, 5 (Br), 6, 7.
4. **Correct IUPAC name**: The name given is correct as per IUPAC rules. Thus, Option C is correct.

### Step 4: Analyze Option D - 2-ethanolhexa-1,5-diene
1. **Identify the structure**: This suggests a hexa (6 carbon chain) with a diene (two double bonds) and an ethanol group.
2. **Draw the structure**:
- Hexa indicates a 6-carbon chain.
- Ethanol suggests an -OH group, which cannot be at position 2 if there are double bonds at positions 1 and 5.
3. **Numbering**: The numbering should prioritize the double bonds over the substituents.
4. **Correct IUPAC name**: The correct name should be 3-methylhexa-1,5-diene. Therefore, Option D is incorrect.

### Conclusion
The correct IUPAC name from the options provided is **Option C - 5-bromo-3-chlorohept-3-ene**.

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