Show how you might use olefin metathesis to assemble the following alkenes from smaller units:
(a)
(b)

Verified step by step guidance

1. Step 1: Identify the target alkene structure. The given structure is a long-chain alkene with a double bond in the middle. Olefin metathesis can be used to assemble this structure by combining smaller alkene units.
2. Step 2: Break the target alkene into two smaller alkene fragments. For example, the target alkene can be divided into two smaller alkenes, each containing half of the carbon chain length and a terminal double bond.
3. Step 3: Select appropriate starting materials. Choose two smaller alkenes that can undergo olefin metathesis to form the desired product. For instance, two terminal alkenes such as 1-hexene and 1-hexene can be used.
4. Step 4: Perform the olefin metathesis reaction. Use a suitable catalyst, such as Grubbs' catalyst, to facilitate the reaction. The catalyst will break and reform the double bonds, creating the desired product.
5. Step 5: Purify the product. After the reaction, isolate and purify the target alkene using techniques such as distillation or chromatography to ensure the desired structure is obtained.

Key Concepts

Olefin Metathesis

Olefin metathesis is a chemical reaction that involves the exchange of alkene fragments to form new alkenes. This reaction is facilitated by catalysts, typically transition metal complexes, which enable the breaking and forming of carbon-carbon double bonds. It is a powerful tool in organic synthesis, allowing for the construction of complex molecules from simpler ones.

Alkene Structure and Reactivity

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, which significantly influences their reactivity. The presence of this double bond makes alkenes more reactive than alkanes, allowing them to participate in various reactions, including addition and metathesis. Understanding the structure of alkenes is crucial for predicting their behavior in chemical reactions.

Catalysts in Organic Reactions

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. In olefin metathesis, specific catalysts, such as Grubbs or Schrock catalysts, are employed to facilitate the reaction between alkenes. The choice of catalyst can significantly affect the efficiency and selectivity of the reaction, making it essential to understand their role in organic synthesis.