page 48 Flashcards
What is steric hindrance in the context of SN2 reactions?
A: Steric hindrance occurs when bulky groups around the carbon bearing the leaving group block the nucleophile’s access, reducing the rate of the SN2 reaction.
Why does methyl bromide undergo SN2 reactions more readily than tert-butyl bromide?
A: Methyl bromide has less steric hindrance because it has no bulky groups attached to the carbon, unlike tert-butyl bromide, which has three bulky methyl groups
How do electrostatic potential maps help in understanding SN2 reactions?
A: They visually represent regions of steric hindrance around the substrate, showing how increasing bulk around the carbon makes nucleophilic attack more difficult.
In SN2 reactions, how does the rate of reaction change with increasing steric hindrance?
A: The rate of the reaction decreases as steric hindrance increases.
What is the relationship between steric hindrance and nucleophilic attack in SN2 reactions?
A: As steric hindrance increases, the nucleophile finds it harder to approach the carbon atom, reducing the reaction rate.
What type of alkyl halides do not undergo SN2 reactions?
A: Tertiary alkyl halides generally do not undergo SN2 reactions due to high steric hindrance.
Why is a backside attack important in SN2 reactions?
A: A backside attack ensures inversion of configuration at the stereogenic center, which is characteristic of SN2 reactions.
Which halide undergoes SN2 reactions the fastest: CH3Br, CH3CH2Br, (CH3)2CHBr, or (CH3)3CBr?
A: CH3Br (methyl bromide) undergoes SN2 reactions the fastest due to minimal steric hindrance.
How does steric hindrance correlate with the rate of an SN2 reaction?
A: The rate of an SN2 reaction is inversely proportional to the steric hindrance of the substrate.
What is the effect of steric hindrance on the transition state in SN2 reactions?
A: Increased steric hindrance raises the activation energy required to form the transition state, reducing the reaction rate.
Why are tertiary alkyl halides more reactive in SN1 reactions than in SN2 reactions?
A: In SN1 reactions, the rate-determining step is carbocation formation, which is stabilized by bulky groups, unlike in SN2 reactions where steric hindrance blocks nucleophilic attack.
Define steric hindrance using the example of methyl bromide vs. tert-butyl bromide.
A: Steric hindrance is the resistance to nucleophilic attack caused by bulky groups. Methyl bromide has no bulky groups, allowing easy attack, while tert-butyl bromide’s three methyl groups block access.
What happens to the configuration of the substrate after an SN2 reaction?
A: The configuration undergoes inversion due to the backside attack mechanism.
Why is backside attack hindered in tertiary alkyl halides?
A: The bulky groups around the carbon block the nucleophile’s approach, preventing the backside attack required for SN2 reactions.
In what order does steric hindrance increase among primary, secondary, and tertiary alkyl halides?
A: Steric hindrance increases in the order: primary < secondary < tertiary
