80 Questions
What is the characteristic of the SN2 nucleophilic substitution mechanism?
It involves a collision-based mechanism with a single transition state.
What type of alkyl halides works well with SN2 nucleophilic substitution?
Methyl or primary alkyl halides
What is the characteristic of the energy diagram of SN2 nucleophilic substitution?
It has one transition state and one activation energy.
What is the characteristic of the SN1 nucleophilic substitution mechanism?
It involves a two-step mechanism with a slow first step and a faster second step.
What type of alkyl halides works well with SN1 nucleophilic substitution?
Tertiary alkyl halides
What is the consequence of steric hindrance in SN2 reactions involving secondary and tertiary alkyl halides?
The reaction rate decreases
What is the geometry of the transition state in the SN2 reaction mechanism?
Trigonal bipyramidal
What is the requirement for the nucleophile to attack the carbon center in an SN2 reaction?
There must be enough space for the attack to be effective
What is the rate law for the SN2 reaction?
Rate = k[RX][Nu:-]
What is the consequence of a negative ΔG in a reaction?
The reaction is spontaneous
What is the characteristic of the transition state in the SN2 reaction mechanism?
Trigonal bipyramidal with partial chemical bonds
Why do tertiary alkyl halides not undergo substitution by the SN2 mechanism?
Due to steric hindrance
What is the rate law for the SN1 reaction mechanism?
Rate = k[RX]
What is the role of a polar solvent in the SN1 reaction mechanism?
To solvate the Br- ion when it detaches
Why do tertiary alkyl halides give faster reactions with the SN1 mechanism?
Due to the stability of the carbocation
What is the preferred mechanism of reaction for primary or methyl alkyl halides?
SN2 mechanism
What is the effect of methyl groups on the stability of a carbocation?
They decrease the positive charge
Which of the following is a characteristic of the SN1 reaction?
It involves a slow first step and a faster second step
What is the effect of increasing the concentration of RX on the rate of an SN1 reaction?
It increases the rate of the reaction
What is the difference between SN1 and SN2 reactions?
SN1 involves a primary or methyl alkyl halide, while SN2 involves a tertiary alkyl halide
What is the result of homolytic cleavage in bond breaking?
Formation of two free radicals
Which type of bond formation is associated with polar reactions?
Heterolytic bond formation
What is a characteristic of a free radical?
It is missing an octet and is very reactive
In an SN2 reaction mechanism, what is the likely effect of steric hindrance on the rate of the reaction?
It decreases the rate of the reaction
What is the result of a free radical seeking another electron in a free radical addition reaction?
The pi bond breaks homolytically
What is the type of reaction that involves heterolytic bond breaking and heterogenic bond formation?
Polar reaction
Which of the following alkyl halides is most likely to undergo an SN1 reaction mechanism?
(CH₃)₃CCl
In an SN2 reaction mechanism, which bond is formed in the rate-determining step?
Carbon-nucleophile bond
What is the order of bond formation and breaking in an SN2 reaction mechanism?
Simultaneous bond breaking and formation
Which of the following factors does not facilitate an SN1 reaction mechanism?
High concentrations of nucleophiles
What is the purpose of using UV light or heat in the initiation step of the free radical addition chain reaction?
To initiate the formation of free radicals
What is the characteristic of the propagation steps in the free radical addition chain reaction?
It produces most of the product formed
What is the reason for the first step being slow in the free radical addition chain reaction?
It involves the breaking of a pi bond
What is the geometry of the carbocation intermediate in the electrophilic addition of HX?
Trigonal planar
What is the characteristic of the termination steps in the free radical addition chain reaction?
They are rare steps in the reaction
What is the purpose of the energy diagram in the free radical addition chain reaction?
To explain why the first step is slow and the second step is fast
What is the role of UV light in the initiation step of the free radical addition chain reaction?
To break down a stable molecule into two free radicals
What is the characteristic of the free radicals in the propagation steps of the free radical addition chain reaction?
They are highly reactive molecules
What is the reason for the second step being fast in the free radical addition chain reaction?
It involves the attack of a fully negative particle on the fully positive carbocation
What is the purpose of the propagation steps in the free radical addition chain reaction?
To produce most of the product formed
What is the primary difference between the SN2 and SN1 reaction mechanisms?
The number of steps involved in the mechanism
Which of the following alkyl halides would be most likely to exhibit steric hindrance in an SN2 reaction?
Tertiary alkyl halide
What is the effect of steric hindrance on the rate of an SN2 reaction?
It decreases the rate of the reaction
Which of the following best describes the mechanism of an SN2 reaction?
A one-step mechanism involving a collision-based reaction
What is the primary reason why tertiary alkyl halides undergo SN1 reactions more easily than SN2 reactions?
They have a more stable carbocation intermediate
What is the reason why tertiary alkyl halides cannot undergo substitution by the SN2 mechanism?
Steric hindrance prevents the nucleophile from attacking the alkyl halide
What is the characteristic of the transition state in the SN2 reaction mechanism?
It has a trigonal bipyramidal geometry with partial chemical bonds
What is the role of the polar solvent in the SN1 reaction mechanism?
It solvates the leaving group, making it more stable
What is the difference between the SN1 and SN2 reaction mechanisms?
The SN1 reaction involves a carbocation intermediate, while the SN2 reaction does not
What is the rate law for the SN1 reaction mechanism?
Rate = k[RX]
What is the significance of the Markovnikov's Rule in electrophilic addition reactions of HX to an alkene?
It dictates the regiospecificity of the reaction
What is the effect of steric hindrance on the SN2 reaction mechanism?
It slows down the reaction
What is the outcome of homolytic cleavage in bond breaking?
Formation of two free radicals
Which type of reaction is characterized by heterolytic bond breaking and heterogenic bond formation?
Polar reaction
What is the characteristic of the transition state in the SN2 reaction mechanism?
Trigonal bipyramidal geometry
What is the effect of steric hindrance on the rate of SN2 reactions?
It decreases the rate of the reaction
Which type of alkyl halides is more likely to undergo an SN2 reaction mechanism?
Primary and methyl alkyl halides
What is the role of the leaving group in the SN2 reaction mechanism?
It is connected to the carbon that is attacked by the nucleophile
Which type of alkyl halides is more likely to undergo an SN2 reaction mechanism?
Primary alkyl halides
What is the role of the nucleophile in an SN2 reaction mechanism?
To form a bond with the carbon center
Which type of alkyl halides reacts through an SN2 mechanism?
Primary or methyl alkyl halides
What is the effect of increasing the concentration of RX on the rate of an SN2 reaction?
It increases the rate
Why do methyl groups donate electron density to the positive C atom in a carbocation?
To reduce the total positive charge
What is the characteristic of the transition state in an SN1 reaction?
It is at a higher energy
What is the effect of steric hindrance on the rate of an SN2 reaction?
It decreases the rate
Which of the following is a characteristic of the transition state in the SN1 reaction mechanism?
A trigonal planar geometry with an empty 2p atomic orbital
What is the effect of steric hindrance on the rate of an SN2 reaction?
It decreases the rate of the reaction
Which of the following alkyl halides is most likely to undergo an SN1 reaction mechanism?
Tertiary alkyl halide
What is the role of the nucleophile in an SN2 reaction mechanism?
It forms a bond with the carbon center before the leaving group leaves
Which of the following is a characteristic of SN2 nucleophilic substitution reactions?
The rate of the reaction is dependent on the concentration of the nucleophile
What is the primary difference between the SN1 and SN2 reaction mechanisms?
The rate-determining step
Which type of alkyl halide is more likely to undergo an SN1 reaction mechanism?
Tertiary alkyl halides
What is the effect of steric hindrance on the rate of an SN2 reaction?
It decreases the rate of the reaction
In an SN2 reaction, what is the order of bond formation and breaking?
Simultaneous bond formation and breaking
What is the role of a polar solvent in an SN1 reaction mechanism?
It stabilizes the carbocation intermediate
Which factor does not facilitate an SN1 reaction mechanism?
Steric hindrance
What is the characteristic of the energy diagram for an SN2 reaction?
It has a single transition state
What is the purpose of using UV light in the initiation step of a free radical addition chain reaction?
To initiate the formation of free radicals
Which of the following alkyl halides is most likely to undergo an SN2 reaction mechanism?
Primary alkyl halides
What is the result of steric hindrance in SN2 reactions involving secondary and tertiary alkyl halides?
It decreases the rate of the reaction
Study Notes
Types of Organic Reactions
- Free radical reactions: involve the formation of free radicals (species with an odd number of electrons)
- Polar reactions: involve the formation of ions
Free Radical Reactions
- Two types:
- Free radical substitution
- Free radical addition
- Free radical addition: a free radical seeking another electron to achieve stability causes the pi bond to break homolytically
- Free radical substitution: involves three distinct steps - initiation, propagation, and termination
- Initiation step: a stable molecule is broken down to two free radicals (slowest step)
- Propagation steps: a free radical attacks a stable molecule and produces another free radical and another stable molecule (faster, most of the product is formed)
- Termination steps: two free radicals react together (rare, very little product is formed)
SN1 Reaction
- Substitution, Nucleophilic, Unimolecular
- Rate Law: Rate = k[RX] (does not depend on the nucleophile concentration)
- First-order reaction
- Mechanism: two-step process
- Step 1: Bond breaks by itself (slow)
- Step 2: Nucleophile attacks carbocation (fast)
- Energy diagram: similar to electrophilic addition of HX to an alkene
- Works best with tertiary alkyl halides
- Factors that facilitate SN1 reaction:
- Increasing [RX]
- Using a polar solvent
- Large X group
SN2 Reaction
- Substitution, Nucleophilic, Bimolecular
- Rate Law: Rate = k[RX][Nu:-] (second-order reaction)
- Mechanism: one-step process
- Nucleophile attacks the carbon that is connected to the leaving group (collision-based reaction)
- Transition state: trigonal bipyramidal geometry
- Works well with methyl or primary alkyl halides
- Factors that facilitate SN2 reaction:
- Increasing [RX] and [Nu]
- Increasing temperature (kinetic energy of collisions)
Carbocation Stability
- A more stable carbocation means a faster Step 1 in SN1 reaction
- Methyl groups donate electron density to the positive C atom, reducing the total positive charge and making the carbocation more stable
- Tertiary carbocation is the most stable, resulting in a faster reaction
Electrophilic Addition of HX to an Alkene
- Reaction intermediate: carbocation (sp2 hybridized, trigonal planar geometry, empty 2p atomic orbital)
- Energy diagram: first step involves the breaking of a pi bond, and this requires energy; second step involves the attack of a fully negative particle (Br-) on the fully positive carbocation
- Markovnikov's Rule: regiospecific reaction, atoms go in specific positions
Learn about the SN2 reaction mechanism, including the energy diagram, transition state, and nucleophile attacks. Understand the formation of the final product and the role of the alkyl halide. Review the key concepts for your chemistry exam.
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