Q8-63 E - Organic Chemistry (Mcmurry)

Question

Simmons–Smith reaction of cyclohexene with diiodomethane gives a single cyclopropane product, but the analogous reaction of cyclohexene with 1,1-diiodoethane gives (in low yield) a mixture of two isomeric methylcyclopropane products. What are the two products, and how do they differ?

Step-by-Step Solution

Answer

Answer

 

Enantiomers, have R and S configurations. 

Step 1: Simmons–Smith reaction

In the Simmons–Smith reaction, diiodomethane reacts with zinc–copper alloy to produce an intermediate I—CH₂Zn—I compound. Iodomethylzinc iodide transfers a CH₂ unit to the alkene in a stereospecific manner. Iodomethylzinc iodide is known as the Simmons–Smith reagent and it is a carbenoid. 

Simmons–Smith reaction is a chelotropic reaction in which an organozinc carbenoid reacts with an alkene or alkyne to form a cyclopropane. 

Step 2: Reaction interpretation

• Simmons–Smith reaction is a stereospecific reaction in which both hydrogens CH₂ are in the same plane.
•  When cyclohexene reacts with 1,1-diiodoethane, it gives a mixture of two isomeric methylcyclopropane products that are enantiomers. They are R and S configurations.
• They are non-superimposable mirror images and rotate plane-polarized light in different directions.

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