page 49 Flashcards
Analysis of the Slide: “Energy Diagrams for SN2 Reactions”
The slide illustrates how the activation energy (Ea) influences the rate of SN2 reactions.
A lower Ea corresponds to a faster reaction, while a higher Ea slows the reaction.
Unhindered alkyl halides, such as CH3Br, have a lower-energy transition state and a lower Ea, leading to faster reactions.
Sterically hindered alkyl halides, such as (CH3)2CHBr, have a higher-energy transition state and higher Ea, resulting in slower reactions.
What is the relationship between activation energy (Ea) and reaction rate in SN2 reactions?
A: A lower Ea leads to a faster reaction rate, while a higher Ea decreases the reaction rate.
Why does CH3Br react faster in an SN2 reaction compared to (CH3)2CHBr?
A: CH3Br is unhindered, resulting in a lower-energy transition state and lower Ea, allowing for a faster reaction.
How does steric hindrance affect the activation energy (Ea) in SN2 reactions?
A: Steric hindrance increases the transition state energy, which raises Ea and slows the reaction rate.
In an SN2 reaction, what happens to the transition state energy as the substrate becomes more sterically hindered?
A: The transition state energy increases, leading to a higher activation energy (Ea).
What is the key difference in energy diagrams for unhindered vs. sterically hindered alkyl halides in SN2 reactions?
A: Unhindered alkyl halides have a lower-energy transition state, while sterically hindered alkyl halides have a higher-energy transition state.
Why does a higher activation energy (Ea) slow down an SN2 reaction?
A: A higher Ea means the reaction requires more energy to reach the transition state, making the reaction slower.
Which alkyl halide would have a lower Ea: CH3Br or (CH3)2CHBr? Why?
A: CH3Br has a lower Ea because it has less steric hindrance, making the nucleophilic attack easier and the transition state lower in energy.
Define the transition state in the context of SN2 reactions.
A: The transition state is a high-energy, unstable arrangement of atoms where partial bonds to both the nucleophile and the leaving group exist.
How does the structure of the alkyl halide affect the energy diagram of an SN2 reaction?
A: Less hindered structures result in lower transition state energy and a lower activation energy (Ea), while more hindered structures raise both.
In the energy diagram of an SN2 reaction, what does the peak of the curve represent?
A: The peak represents the transition state, which is the highest-energy point in the reaction pathway.
What role does the nucleophile play in lowering Ea in an SN2 reaction?
A: A strong nucleophile can stabilize the transition state, effectively lowering Ea and speeding up the reaction.
Compare the reaction rates of primary and secondary alkyl halides in SN2 reactions in terms of Ea.
A: Primary alkyl halides have lower Ea and faster reaction rates, while secondary alkyl halides have higher Ea and slower reaction rates.
Why do tertiary alkyl halides not typically undergo SN2 reactions?
A: Tertiary alkyl halides have extreme steric hindrance, raising Ea to impractical levels and preventing the nucleophile’s backside attack.
How does the leaving group influence the energy diagram in SN2 reactions?
A: A good leaving group stabilizes the transition state, lowering Ea and making the reaction faster.
In SN2 reactions, what structural features lead to a slower reaction as seen in the energy diagram?
A: Increased steric hindrance around the reactive center leads to a higher transition state energy and slower reaction rate.
