Explore key concepts of organic chemistry reactions and mechanisms with these medium-level questions, covering substitution, elimination, addition, and rearrangement processes. Perfect for students and enthusiasts aiming to reinforce their understanding of core organic reaction pathways and mechanisms.
Which factor most strongly favors an SN1 reaction mechanism over SN2 for the hydrolysis of alkyl halides, such as the hydrolysis of tert-butyl bromide in water?
Explanation: SN1 reactions are favored by steric hindrance because the rate-determining step is formation of a carbocation, which is stabilized by bulky groups like in tert-butyl. In contrast, strong nucleophiles and primary alkyl halides favor SN2, since SN2 is a single-step, backside attack sensitive to sterics. Aprotic solvents favor SN2, not SN1. Therefore, strong steric hindrance is key for SN1.
What is the major product when benzene reacts with bromine in the presence of iron(III) bromide (FeBr3) catalyst?
Explanation: The electrophilic aromatic substitution of benzene with bromine and FeBr3 produces bromobenzene as the major product, with bromine substituting a hydrogen atom on the ring. 1,3-Dibromobenzene would only form with excess bromine and specific conditions. Cyclohexyl bromide and toluene are unrelated: cyclohexyl bromide is from an alkane and toluene is methylbenzene, not a halogenated product.
When propene is treated with HBr, which carbon atom receives the bromine according to Markovnikov's rule?
Explanation: Markovnikov's rule dictates that in the addition of HX to an alkene, the hydrogen adds to the less substituted carbon and the halide adds to the more substituted carbon, stabilizing the intermediate. Bromine, therefore, attaches to the secondary, more substituted carbon. Peroxide presence reverses this (anti-Markovnikov), so the peroxide answer is only sometimes correct. The reaction does not proceed equally to both or mainly to the primary carbon under standard conditions.
In an E2 elimination reaction, which geometric relationship between the leaving group and the hydrogen being abstracted is required for the reaction to proceed efficiently?
Explanation: E2 eliminations require the leaving group and the hydrogen being removed to be anti-coplanar, maximizing orbital overlap in the transition state. Syn-coplanar is less favorable due to steric and geometric constraints. Geminal describes two groups on the same carbon, which is not relevant here. Cis orientation refers to generic arrangement and is not specific enough for the E2 requirement.
During the acid-catalyzed hydration of 3,3-dimethyl-1-butene, what type of rearrangement is most likely to occur after the initial carbocation forms?
Explanation: In the hydration of 3,3-dimethyl-1-butene, the initially-formed carbocation is secondary and can undergo a hydride shift to become a more stable tertiary carbocation. Methyl migration is less likely due to the hydride's proximity. Alkoxide elimination is not a carbocation rearrangement. Ring expansion cannot occur because the substrate does not contain a cycloalkyl ring.