Question

Identify the functional group and parent chain. Number the parent chain. Determine the IUPAC name. Determine stereochemistry of the double bond.

• A. (E)-5-ethyl-2-methylhept-3-en-3-ol
• B. (Z)-5-ethyl-2-methylhept-3-en-3-ol
• C. 5-ethyl-2-methylhept-3-en-3-ol
• D. 2-ethyl-5-methylhept-3-en-3-ol

Answer 1

Answer: (A)

(E)-5-ethyl-2-methylhept-3-en-3-ol

Answer 2

The molecule contains a hydroxyl (-OH) group and a carbon-carbon double bond. The longest continuous carbon chain including the hydroxyl group is a 7-carbon chain (heptene). Numbering starts from the end that gives the lowest locant to the hydroxyl group, which is carbon 3. The double bond is between carbons 3 and 4. There is a methyl substituent on carbon 2 and an ethyl substituent on carbon 5. The parent chain is therefore hept-3-ene. The hydroxyl group is on carbon 3, making it hept-3-en-3-ol. The substituents give the name 5-ethyl-2-methylhept-3-en-3-ol.

To determine the stereochemistry of the double bond (between C3 and C4): On C3, the groups are -OH and -CH(CH3)2. Priority: -OH > -CH(CH3)2. On C4, the groups are -CH3 and -CH(CH2CH3). Priority: -CH(CH2CH3) > -CH3. In the given structure, the higher priority groups (-OH on C3 and -CH(CH2CH3) on C4) are on opposite sides of the double bond. Therefore, the configuration is E (entgegen).

The full IUPAC name is (E)-5-ethyl-2-methylhept-3-en-3-ol.