30 Questions
What is the principle that dictates the direction of a chemical reaction according to transition-state theory?
The lowest energy pathway available
Which type of reaction involves substitution at the metal center in coordination complexes?
Substitution at the metal center
What imposes variability on the reactivity of coordination complexes?
Metal atoms
In free energy coordinate diagrams, what is the adopted path between the reactants and products?
The lowest energy pathway available
What do transition-state theory describes chemical reactions as moving between?
Reactants and transition states
What is the highest energy structure along a reaction pathway called?
Transition state
How are transition states different from intermediates?
Intermediates have extended and weaker bonds compared to reactants, while transition states do not.
What do reaction coordinate diagrams help to explain?
Mechanism of reaction
What does the principle of microscopic reversibility state?
The adopted pathway between reactants and products is the same regardless of the direction of the reaction.
What is a classic example of a substitution reaction involving [Fe(H2O)6] and SCN-?
[Fe(H2O)6] + NaCl
Which type of ligands tend to make complexes inert?
Strong-field ligands
What determines whether a substitution reaction is classified as dissociative (D) or associative (A)?
The coordination number of the intermediate formed
Which metal ions have the fastest water exchange rates among the given options?
[Fe(H2O)6]3+
What color does the initial solution turn due to the presence of Fe(III) complexes?
Yellow
What are 'labile' and 'inert' in the context of complexes?
Kinetic terms used to describe reaction rates
Which type of interchange intermediate forms when the incoming ligand begins forming a bond to the central atom before the departing ligand bond is weakened?
Associative interchange intermediates (Ia)
Which type of interchange intermediate appears when the degree of assistance is small and the reaction is primarily dissociative?
Interchange intermediates (Id)
What type of reactions typically involve a 7-coordinate intermediate and a higher coordination number?
Associative reactions
In which type of interchanges do 5-coordinate intermediates commonly occur?
Dissociative reactions
What are the categories of dissociative, associative, and interchange mechanisms known as?
Stoichiometric mechanisms
What defines a dissociative (D) mechanism in coordination reactions?
The leaving group dissociates first from the complex before the incoming group binds
What is a characteristic of an interchange (I) mechanism in coordination reactions?
The incoming group directly replaces the leaving group in the complex without intermediate formation
What provides evidence for a dissociative (D) mechanism in coordination reactions?
Dependence of the reaction rate on the concentration of both reactants, X and Y
What limitation exists in detecting interchange mechanisms in coordination reactions?
Lack of evidence for an intermediate in many cases
How can experimental data exhibiting both interchange and substitution mechanisms be interpreted in coordination reactions?
As evidence for the validity of both mechanisms
Which type of reaction involves substitution at the metal center in coordination complexes?
Associative interchange mechanism
What influences the kinetics of dissociative substitution reactions?
LFAE values
What is the significance of the highest LFAE values (most positive) in coordination complexes?
Inertness of ions
What results in second-order kinetics for the associative interchange mechanism?
Steady-state approximation
What is the function of the splitting of d-based levels from octahedral to square-planar symmetry in the transition state?
Distance and angle changes influence
Study Notes
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The highest energy structure along a reaction pathway is called the transition state.
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Transition states are unstable and are not detectable intermediates.
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The reaction process proceeds through a transition state without a detectable intermediate state.
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Intermediates, in contrast, are detectable and they have extended bonds and weaker bonds compared to the reactants.
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The reaction coordinate diagrams help to explain the reaction mechanism and the extent of reaction.
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The energy profiles of reactions can be determined through kinetics experiments to find the activation energy and its components.
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The principle of microscopic reversibility states that the adopted pathway between reactants and products is the same regardless of the direction of the reaction.
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The pressure dependence on reaction rates provides insight into the volume of activation and the size of the transition state.
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Large activation energies hinder the reaction rate, but large equilibrium constants favor the reaction.
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Substitution reactions are common in coordination chemistry, where metal ions like [M(H2O)m] are involved as reactants.
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Substitution reactions can produce colored products to identify metal ions and are generally rapid.
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Fe(H2O)6 + SCN- is a classic example of a substitution reaction involving [Fe(H2O)6] and SCN-.
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Other ligand species like HNO3, NaCl, H3PO4, KSCN, and NaF can be added to a solution of Fe(NO3)3.9H2O to observe the reaction.
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If the interchange reaction is reversible, it can be approximated as a pair of opposing pseudo-first order reactions.
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In an associative interchange mechanism, the I (incoming ligand) and D (departing ligand) bonds are broken and formed in the transition state.
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In a dissociative interchange mechanism, the I (incoming ligand) bond is more important in the transition state.
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The transition state of associative interchange involves the formation of an intermediate with an increased coordination number.
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The steady-state approximation results in second-order kinetics for the associative interchange mechanism.
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The kinetics of dissociative substitution reactions are influenced by various factors, including LFAE values.
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The highest LFAE values (most positive) are associated with inert ions such as d3 and low-spin d4, d5, and d6.
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The negative LFAE parameters predict low activation barriers for an octahedral complex losing a ligand.
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The splitting of d-based levels from octahedral to square-planar (SQP, C4v) symmetry is a function of the distance and angle changes in the transition state.
Test your knowledge of inorganic chemistry reaction intermediates with this quiz. Identify and understand different types of intermediates and their roles in chemical reactions.
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