Question

The IUPAC name of the following compound is -

• A. 4-Hydroxyhept-1-en-6-yne
• B. 4- Hydroxyhept-6-en-1-yne
• C. Hept-6-en-1-yn-4-ol
• D. Hept-1-en-6-yn-4-ol

Answer 1

Answer: (D)

Hept-1-en-6-yn-4-ol

Answer 2

1. Identify the Principal Functional Group: The compound contains an alcohol (-OH), an alkene (C=C), and an alkyne (C≡C). According to IUPAC priority rules, the alcohol group (-OH) is the principal functional group. Therefore, the name will end with "-ol".

2. Identify the Longest Carbon Chain: The longest carbon chain containing the principal functional group (-OH) has 7 carbon atoms. Thus, the parent hydrocarbon is heptane.

3. Number the Carbon Chain: The numbering of the carbon chain is done to give the lowest possible locant to the principal functional group (-OH). Let's analyze the structure: HC≡C-CH₂-CH(OH)-CH₂-CH=CH₂

   • Numbering from left to right: 1 2 3 4 5 6 7 HC≡C-CH₂-CH(OH)-CH₂-CH=CH₂ The -OH group is at position 4. The alkyne starts at position 1. The alkene starts at position 6.

   • Numbering from right to left: 7 6 5 4 3 2 1 CH₂=CH-CH₂-CH(OH)-CH₂-C≡CH The -OH group is at position 4. The alkene starts at position 1. The alkyne starts at position 6.

4. Apply Priority Rules for Unsaturated Bonds: Since the -OH group is at position 4 in both numbering schemes, we must apply the rule for compounds containing both double and triple bonds: "Number the chain to give the lowest locant to the double bond (alkene)."

   • Numbering from the right gives the alkene the locant 1.
   • Numbering from the left gives the alkene the locant 6.

   Therefore, numbering from the right is correct.

5. Construct the IUPAC Name:

   • Parent chain: Heptane.
   • Principal functional group: Alcohol at position 4, so "-4-ol".
   • Unsaturated bonds: Alkene at position 1 ("-1-en-") and alkyne at position 6 ("-6-yne").

   Combining these, the IUPAC name is Hept-1-en-6-yn-4-ol.

6. Match with Options: This name corresponds to option (4).

   Let's briefly check why other options are incorrect:

   • Options (1) and (2) treat the hydroxyl group as a substituent ("4-Hydroxy..."). This is incorrect because the alcohol group has higher priority than alkene and alkyne and should determine the suffix.
   • Option (3) "Hept-6-en-1-yn-4-ol" implies numbering from the left, which gives the alkyne a locant of 1 and the alkene a locant of 6. This is incorrect according to the rule that the alkene should get the lower locant when the principal functional group is at the same position.