Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.


(a) 5-methylhex-1-ene

Verified step by step guidance

1. Identify the structure of the target molecule, 5-methylhex-1-ene, which is a six-carbon chain with a methyl group on the fifth carbon and a double bond between the first and second carbons.
2. Recognize that an allylic halide is a compound where a halogen is attached to a carbon atom adjacent to a carbon-carbon double bond.
3. Select an appropriate allylic halide that can be used to form the desired carbon skeleton. For 5-methylhex-1-ene, consider using 4-bromo-2-methylpent-1-ene as the allylic halide.
4. Choose a Grignard reagent that will add the necessary carbon atoms to complete the hydrocarbon chain. In this case, use methylmagnesium bromide (CH₃MgBr) to add a methyl group.
5. Perform the reaction by treating the allylic halide with the Grignard reagent, which will result in the formation of the desired hydrocarbon, 5-methylhex-1-ene, through a nucleophilic substitution mechanism.

Key Concepts

Allylic Halides

Allylic halides are organic compounds where a halogen atom is bonded to an allylic carbon, which is adjacent to a carbon-carbon double bond. This positioning makes them reactive in nucleophilic substitution reactions, allowing for the formation of new carbon-carbon bonds when reacted with nucleophiles like Grignard reagents.

Grignard Reagents

Grignard reagents are organomagnesium compounds represented as R-MgX, where R is an organic group and X is a halogen. They are powerful nucleophiles that can react with electrophiles to form new carbon-carbon bonds, making them essential in organic synthesis for constructing complex molecules.

Synthesis of Alkenes

The synthesis of alkenes often involves the formation of double bonds through elimination reactions or the addition of nucleophiles to allylic halides. In this context, the reaction of an allylic halide with a Grignard reagent can lead to the formation of a new alkene by creating a carbon chain that can subsequently undergo elimination to yield the desired alkene product.