Question

The IUPAC name of the following compound is

• A. 3-Methenyl-6-methyloct-7-yn-5-ol
• B. 2-Ethyl-5-methylhept-1-en-6-yn-4-ol
• C. 2-Ethyl-5-methylhept-1-yn-6-en-4-ol
• D. 3-Methyl-6-ethylhept-6-en-1-yn-4-ol

Hint:

IUPAC Naming Priority Order for this problem: 1. Suffix (-ol for alcohol). Give this the lowest possible number. 2. Multiple bonds (-en, -yn). If tie for -ol, give these the lowest numbers. 3. If still a tie, give -en priority over -yn. 4. Prefixes (substituents like methyl, ethyl). Give these the lowest numbers only after satisfying the above rules. List them alphabetically.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question requires the application of IUPAC nomenclature rules for an organic compound containing multiple functional groups (alcohol, alkene, alkyne) and substituents.
Step 2: Applying IUPAC Rules:
1. Identify the Principal Functional Group: The compound contains an alcohol (-OH), a double bond (-C=C-), and a triple bond (-C≡C-). According to IUPAC priority rules, the alcohol group is the principal functional group, so the suffix of the name will be "-ol".
2. Identify the Parent Carbon Chain: The parent chain must be the longest possible carbon chain that contains the principal functional group (-OH) and the maximum number of multiple bonds. By inspection, the longest such chain contains 7 carbon atoms. So, the parent alkane is heptane.
3. Number the Parent Chain: The chain must be numbered to give the lowest possible locant (number) to the principal functional group (-OH). Numbering from either end gives the -OH group position 4. When there is a tie, the next priority is given to the multiple bonds. Both numbering schemes give the set of locants {1, 6} for the multiple bonds. In case of a further tie, the double bond is given priority over the triple bond. Therefore, we number from the left end to give the double bond the lower number (1).
The correct numbering is: \[ \overset{1}{\text{C}}\text{H}_2=\overset{2}{\underset{\text{CH}_2\text{CH}_3}{\underset{|}{C}}}-\overset{3}{\text{C}}\text{H}_2-\overset{4}{\underset{\text{OH}}{\underset{|}{C}}}\text{H}-\overset{5}{\underset{\text{CH}_3}{\underset{|}{C}}}\text{H}-\overset{6}{\text{C}}\equiv\overset{7}{\text{C}}\text{H} \] 4. Identify and Name Substituents: - At position 2, there is an ethyl group. - At position 5, there is a methyl group. - At position 4, there is the principal hydroxyl group. - At position 1, there is a double bond (-en). - At position 6, there is a triple bond (-yn).
5. Assemble the Name: - Substituents in alphabetical order: 2-Ethyl-5-methyl - Parent chain with multiple bonds: hept-1-en-6-yn - Principal functional group: -4-ol - Combining them gives: 2-Ethyl-5-methylhept-1-en-6-yn-4-ol
Step 3: Final Answer:
The correct IUPAC name is 2-Ethyl-5-methylhept-1-en-6-yn-4-ol. This matches option (B).