For each synthesis, start with bromocyclohexane and predict the products. Assume that an excess of each reactant is added so that all possible reactions that can happen will happen. (c)
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Step 1: Analyze the first reaction. Bromocyclohexane reacts with KOH in ethanol under heat (Δ). This is an elimination reaction where KOH acts as a base, removing a β-hydrogen from bromocyclohexane. The result is the formation of cyclohexene (compound A) via an E2 mechanism.
Step 2: Examine the second reaction. Cyclohexene (A) reacts with mCPBA (meta-chloroperoxybenzoic acid), which is a peracid. This reaction is an epoxidation, where the double bond in cyclohexene reacts with mCPBA to form an epoxide (compound H).
Step 3: Consider the third reaction. The epoxide (H) reacts with PhMgBr (phenylmagnesium bromide, a Grignard reagent) in ether. Grignard reagents attack the less substituted carbon of the epoxide, opening the ring and forming an alcohol intermediate after hydrolysis with dilute H3O+ (compound I).
Step 4: Analyze the final reaction. The alcohol (I) undergoes dehydration in the presence of H2SO4 under heat (Δ). This is an elimination reaction where H2SO4 acts as a catalyst, removing water to form an alkene (compound J).
Step 5: Summarize the sequence. The reactions involve elimination, epoxidation, nucleophilic attack by a Grignard reagent, and dehydration. Each step transforms the starting bromocyclohexane into progressively different functional groups, leading to the final alkene product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. In the case of bromocyclohexane, the bromine atom acts as a leaving group, allowing nucleophiles to attack the carbon atom it was attached to. Understanding the mechanism (SN1 or SN2) is crucial for predicting the products of the reaction.
Nucleophiles and Electrophiles can react in Substitution Reactions.
Electrophilic Addition
Electrophilic addition is a reaction where an electrophile reacts with a nucleophile, leading to the formation of a more saturated product. In the context of bromocyclohexane, if a double bond is present in the reactants, the bromine can add across the double bond, resulting in a new product. Recognizing the nature of the reactants helps in predicting the outcome of the reaction.
Alkyl halides, such as bromocyclohexane, are reactive due to the polar C-X bond, where X is a halogen. The reactivity can vary based on the structure of the alkyl group (primary, secondary, or tertiary) and the type of reaction (substitution or elimination). Understanding these factors is essential for predicting how bromocyclohexane will react with different nucleophiles or electrophiles.