Question

IUPAC name of the following CH2 = CH – CH2 – CH2 – C ≡ CH is 

• A. 1, 5-hexenyne
• B. 1-hexene-5-yne
• C. 1-hexyne-5-ene
• D. 1, 5-hexynene

Answer 1

The Correct Option is B

The IUPAC naming of organic compounds follows a systematic approach to ensure consistency. For the given compound CH_2 = CH - CH_2 - CH_2 - C \equiv CH, let's determine the correct IUPAC name.

1. First, identify the longest carbon chain that includes the maximum number of multiple bonds. In this compound, the longest chain containing both double and triple bonds has 6 carbon atoms.

2. Number the chain starting from the end nearest to the first point of difference, which in this case is the double bond. Begin numbering from the ethene end:

   • Carbon 1: CH_2 (double bond)
   • Carbon 2: CH (double bond)
   • Carbon 3: CH_2
   • Carbon 4: CH_2
   • Carbon 5: C (triple bond)
   • Carbon 6: CH (triple bond)

3. Now, identify the locants for the double and triple bonds. The double bond is at position 1, and the triple bond is at position 5.

4. The suffixes for a double and a triple bond are "-ene" and "-yne," respectively. When both are present, the double bond suffix "-ene" comes before "-yne."

5. Thus, the name is formed by combining these parts: 1-hexene-5-yne.

Therefore, the correct IUPAC name for the compound is 1-hexene-5-yne. Let's further justify why other options are incorrect:

• 1, 5-hexenyne: Improper use of positional numbers together.
• 1-hexyne-5-ene: Incorrect order of suffixes; "-ene" should come before "-yne".
• 1, 5-hexynene: Improper use of positional numbers and incorrect order of suffixes.