Which of the following methods is the most efficient synthesis of $\left(Z\right)-3-\mathrm{heptene}$?

• A. Dehydrohalogenation of 3-bromoheptane with strong base
• B. E2 elimination of 3-chloroheptane with sodium ethoxide in ethanol
• C. Partial hydrogenation of $3-\mathrm{heptyne}$ using sodium in liquid ammonia
• D. Partial hydrogenation of $3-\mathrm{heptyne}$ using Lindlar's catalyst

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the target molecule, (Z)-3-heptene, which is a cis-alkene with the double bond between carbons 3 and 4 in a seven-carbon chain. The (Z) configuration means the higher priority groups on each carbon of the double bond are on the same side.
2. Step 2: Analyze the first two methods involving elimination reactions (dehydrohalogenation and E2 elimination). These methods typically produce a mixture of E and Z isomers due to the nature of elimination mechanisms and the lack of stereoselectivity, making it difficult to selectively obtain the (Z) isomer.
3. Step 3: Consider the partial hydrogenation of 3-heptyne. Alkynes can be selectively reduced to alkenes using specific catalysts. Sodium in liquid ammonia typically gives the trans (E) alkene via a dissolving metal reduction, which is not the desired (Z) isomer.
4. Step 4: Recognize that Lindlar's catalyst is a poisoned palladium catalyst that selectively hydrogenates alkynes to cis (Z) alkenes without further reduction to alkanes. This method allows for stereoselective synthesis of (Z)-3-heptene from 3-heptyne.
5. Step 5: Conclude that the most efficient and stereoselective method to synthesize (Z)-3-heptene is the partial hydrogenation of 3-heptyne using Lindlar's catalyst, as it directly produces the desired (Z) alkene with high selectivity.