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Questions and Answers
What occurs first in an outer-sphere redox reaction?
What occurs first in an outer-sphere redox reaction?
- Electron transfer
- Dissociation of successor complex
- Formation of precursor complex (correct)
- Activation/reorganization of precursor complex
What primarily affects the rate constant in an outer-sphere redox reaction?
What primarily affects the rate constant in an outer-sphere redox reaction?
- Type of solvent used
- Concentration of reactants
- Temperature of the reaction
- Electronics and geometrical structures of reactants (correct)
Which factor is NOT involved in the Gibbs energy changes during the reaction?
Which factor is NOT involved in the Gibbs energy changes during the reaction?
- Changes in metal-ligand bond lengths
- Reorganization of the precursor complex
- Energy required to reorganize the solvent
- Dissociation of the product (correct)
Why do electron transfer reactions require geometric restructuring of reactants?
Why do electron transfer reactions require geometric restructuring of reactants?
What role do solvent interactions play in outer-sphere redox reactions?
What role do solvent interactions play in outer-sphere redox reactions?
According to the Frank-Condon principle, what is the relationship between electronic transitions and nuclear movement?
According to the Frank-Condon principle, what is the relationship between electronic transitions and nuclear movement?
What is the outcome when reactants achieve equal orbital energies at the activation transition state?
What is the outcome when reactants achieve equal orbital energies at the activation transition state?
Which statement is true regarding the electron transfer process in a redox reaction?
Which statement is true regarding the electron transfer process in a redox reaction?
What characterizes an inner-sphere redox reaction?
What characterizes an inner-sphere redox reaction?
Which step is most commonly rate-determining in an inner-sphere redox reaction?
Which step is most commonly rate-determining in an inner-sphere redox reaction?
In an outer-sphere redox reaction, what is true?
In an outer-sphere redox reaction, what is true?
Which statement is true about the bridging ligand in inner-sphere reactions?
Which statement is true about the bridging ligand in inner-sphere reactions?
What could be a rate-limiting step in an inner-sphere redox reaction?
What could be a rate-limiting step in an inner-sphere redox reaction?
Electron transfer in inner-sphere reactions is sensitive to which of the following?
Electron transfer in inner-sphere reactions is sensitive to which of the following?
What is a unique feature of the electron transfer process in inner-sphere mechanisms?
What is a unique feature of the electron transfer process in inner-sphere mechanisms?
Which factor affects the rate of the electron-transfer step in inner-sphere reactions?
Which factor affects the rate of the electron-transfer step in inner-sphere reactions?
What type of entities often require geometric organization before linking occurs?
What type of entities often require geometric organization before linking occurs?
What advantages do metal complexes provide in synthetic chemistry?
What advantages do metal complexes provide in synthetic chemistry?
Which metal ion is specified for templating in the synthesis of crown ethers?
Which metal ion is specified for templating in the synthesis of crown ethers?
What is a notable attribute of crown ether syntheses involving alkali metals?
What is a notable attribute of crown ether syntheses involving alkali metals?
What is the process called when two alkyl groups are added to a dithiolate using a metal ion as a template?
What is the process called when two alkyl groups are added to a dithiolate using a metal ion as a template?
In the context of template reactions, what is often a challenge related to alkali metals?
In the context of template reactions, what is often a challenge related to alkali metals?
What does a high value of $k_{N3-} / k_{NCS-}$ indicate about the reaction mechanism?
What does a high value of $k_{N3-} / k_{NCS-}$ indicate about the reaction mechanism?
Which of the following best describes 18-Crown-6 in the context of synthesis?
Which of the following best describes 18-Crown-6 in the context of synthesis?
Which equation can predict the rate constants for outer-sphere electron transfer reactions?
Which equation can predict the rate constants for outer-sphere electron transfer reactions?
What is a common characteristic of many template reactions mentioned?
What is a common characteristic of many template reactions mentioned?
How does complexation affect the electronic structure of the reactants?
How does complexation affect the electronic structure of the reactants?
What is represented by $Z$ in the equations discussed?
What is represented by $Z$ in the equations discussed?
What factor primarily determines the Gibbs energy of activation, ∆‡G, in electron transfer between [Fe(OH2)6]3 and [Fe(OH2)6]2?
What factor primarily determines the Gibbs energy of activation, ∆‡G, in electron transfer between [Fe(OH2)6]3 and [Fe(OH2)6]2?
What role does a template play in a reaction assembly?
What role does a template play in a reaction assembly?
What does the effective collision frequency relate to?
What does the effective collision frequency relate to?
Which of the following statements explains why electron transfer is generally faster for 2nd and 3rd row metals than for 1st row metals?
Which of the following statements explains why electron transfer is generally faster for 2nd and 3rd row metals than for 1st row metals?
Which condition is NOT relevant for determining if electron transfer is an outer or inner sphere mechanism?
Which condition is NOT relevant for determining if electron transfer is an outer or inner sphere mechanism?
What does the term 'template reaction' refer to?
What does the term 'template reaction' refer to?
What role do ligands with extended π-systems play in electron transfer?
What role do ligands with extended π-systems play in electron transfer?
In the context of electron transfer, what is reorganization energy?
In the context of electron transfer, what is reorganization energy?
How can one determine whether a ligand has a bridging capability in an electron transfer process?
How can one determine whether a ligand has a bridging capability in an electron transfer process?
What happens to the activation energy for electron exchange when [Fe(OH2)6]3 and [Fe(OH2)6]2 possess different nuclear configurations?
What happens to the activation energy for electron exchange when [Fe(OH2)6]3 and [Fe(OH2)6]2 possess different nuclear configurations?
In the context of thermal fluctuations, what does the point of intersection of the potential energy curves represent?
In the context of thermal fluctuations, what does the point of intersection of the potential energy curves represent?
Which of the following best defines the role of a photon in electron transfer mechanisms?
Which of the following best defines the role of a photon in electron transfer mechanisms?
Study Notes
Redox Reactions
- Inner Sphere (IS): A ligand is shared between two reactants forming a transition state.
- Outer Sphere (OS): No bridging ligand between reacting species.
Inner Sphere Mechanism
- Precursor Complex: Formed by the first step in an inner-sphere reaction.
- Bridged Binuclear Intermediate: Formed in the second step.
- Electron Transfer: Occurs via the bridging ligand.
- Rate-determining Step: Can be any step, but the electron-transfer step is the most common.
- Dissociation: Breakup of the bridged complex is rate-determining if both metal ions have a nonlabile electron configuration.
- Ligand Transfer: Can be a two-step process (metal to ligand then ligand to metal).
- Sensitivity to Ligands: Inner-sphere electron transfer is very sensitive to the bridging ligand.
Outer Sphere Mechanism
- Mechanism: Involves electron tunneling between reactants without any significant covalent bond disruptions or inner-coordination sphere changes.
- Rate Constant: Depends on:
- Electronic and geometric structures of reactants.
- Gibbs energy of reaction.
- Mechanism Steps:
- Formation of precursor complex.
- Activation/reorganization of precursor.
- Electron transfer.
- Relaxation to successor complex.
- Dissociation of the successor complex.
- Electron Transfer: The slowest step.
- Nuclear Configuration: Reactants must achieve the same nuclear configuration (e.g., bond lengths) to facilitate electron transfer. This requires thermal activation and leads to activation energy (∆‡G).
Factors Influencing Electron Transfer Rates
- Solvent: Solvents that strongly interact with complexes (hydrogen bonding) will reduce the rate of electron transfer.
- Metal-Ligand Bond Lengths: Changes in oxidation state of the metal affect bond lengths.
- Frank-Condon Principle: Nuclei can't immediately respond to electron transfer so complexes must adjust before electron transfer occurs.
- Orbital Energies: Orbital energies must be equal for electron transfer to occur.
Second and Third Row Transition Metals
- Faster Electron Transfer Rates: Compared to first-row metals due to better overlap of 4d and 5d orbitals.
- Stronger Ligand Fields: Lead to smaller bond length distortions.
- π-Systems: Ligands with extended π-systems (e.g., Phen, bipy) can assist electron transfer.
Distinguishing Inner and Outer Sphere Mechanisms
- Vacant Coordination Site: Present in inner sphere mechanism.
- Labile Reactant: May indicate preference for inner sphere mechanism.
- Ligand Transfer: Occurs in the inner sphere.
- Effect of Bridging Ligands: Large differences in rate upon addition or substitution of bridging ligands suggest an inner-sphere mechanism.
- N3- and NCS- Complexes: Comparing rates of electron transfer between N3- and NCS- complexes can be helpful:
- Rate ratios near 1 (~1) typically indicate an outer sphere mechanism.
- Large rate ratios (>>1) suggest an inner sphere mechanism.
- N3- is symmetric and facilitates inner sphere.
Marcus Equation
- Prediction of Rates: Can be used to predict rate constants for outer-sphere electron transfer reactions.
- Cross Relation: Relating rates of electron transfer between different species.
- Reorganization Energy: The average of the values for the two self-exchange processes.
Template Reactions
- Features:
- Complex Formation: Brining reactants closer together in the correct orientation.
- Electronic Structure: Complexiation changes the electronic structure, promoting reaction.
- Examples:
- Dialkylation of nickel dithiolates.
- Synthesis of phthalocyanin.
- Alkali metal-templated syntheses of crown ethers.
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Description
Explore the fascinating world of redox reactions, focusing on the inner sphere and outer sphere mechanisms. This quiz covers the formation of precursor complexes, electron transfer processes, and the role of bridging ligands in these reactions. Test your understanding of these essential concepts in electrochemistry!
