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eCHM3941 > INORGANIC SUBSTITUTION > Flashcards

INORGANIC SUBSTITUTION Flashcards

(44 cards)

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1
Q

What is thermodynamics

A

Questioning whether the reaction will happen at all

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2
Q

What is kinetics

A

Questioning how fast the reaction will occur

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3
Q

When are forward and backwards rates equal

A

At equilibrium

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4
Q

Why does the rate of the forward reaction have a negative coefficient

A

As this will cancel out the depletion of the reactant.

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5
Q

What does rate (forward) equal

A

-d[A]/dt = kf[A][B]

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6
Q

What does rate (backward) equal

A

d[A]/dt = kb[C][D]

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7
Q

kf / kb =

A

K

equilibrium constant

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8
Q

What does inert mean

A

slow rate of decomposition

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9
Q

What does labile mean

A

More rapid equilibration

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10
Q

Can a reactant be unstable and inert?

A

Yes, can be unstable thermodynamically, but kinetically the reaction is so slow that it is considered inert

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11
Q

What are the characteristics of an inert complex

A

high charge density

small bond length/ high bond strength

high stability (low LFSE, chelate effect, no distortion)

small ion size

not s block (except for Be2+ and Mg2+)

4d and 5d (not 3d)

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12
Q

What is a dissociative mechanism. Is intermediate detectable?

A

dissociation occurs first

Intermediate detectable

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13
Q

What is an associative mechanism. Is intermediate detectable?

A

association occurs first

Intermediate detectable

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14
Q

What is an interchange mechanism. Is intermediate detectable?

A

Dissociation and association occur at the same time

Intermediate not detectable

(Energy profile has association first)

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15
Q

What does associatively activated mean

A

Rate determining step is association

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16
Q

What does dissociatively activated mean

A

Rate determining step is dissociation

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17
Q

Why aren’t intermediates detectable for Aa or Dd mechanisms

A

The first step of each is activated. Therefore the high energy means the intermediate forms and unforms so quickly that it is undetectable

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18
Q

In general

1st order

2nd order

mechanism…

Study These Flashcards
A

1st order: generally D or Id

2nd order: generally A or Ia

19
Q

What is the rate of a square planar substitution? What is the equation

Study These Flashcards
A

Pseudo first order

kobs[metal]

kobs = k1 + k2[ligand]

20
Q

What is a nucleophilicity parameter

Study These Flashcards
A

Defined in terms of the reaction rates of a specific platinum complex.

Increase means that nucleophile will increase reaction rate

21
Q

What are the characteristics of a hard lewis acid

Study These Flashcards
A

small radii

high positive charge

high energy LUMOs

22
Q

What are the characteristics of a hard lewis base

Study These Flashcards
A

small radii

high electronegativity

high energy HOMOs

23
Q

What are the characteristics of a soft lewis acid

Study These Flashcards
A

large radii

low positive charge

low energy LUMOs

24
Q

What are the characteristics of a soft lewis base

Study These Flashcards
A

large radii

moderate electronegativity

low energy HOMOs

25
What are the 3 factors on a square planar reaction
nucleophilicity of entering group trans effect steric effects
26
Explain the trans effect
Trans influence: trans ligands that are good sigma donors cause weakening of other trans bond encouraging dissociation Transition state effect: entering ligands with goof pi acceptance can accomodate electron density and therefore better at association
27
Explain the steric effects on a square planar reaction
steric crowding blocks nucleophiles therefore, inhibits associative mechanism and favours dissociative mechanism. Sterics on trans to substitution site is better than cis
28
Explain the stereochemistry of a square planar substitution
Passes through a trigonal bipyramidal transition state Preserves original geometry two cis ligands are out of trigonal plane and therefore don't affect in reaction
29
What sign of S and V show associative mechanism
negative
30
What are the most common mechanism of octahedral substitution and why
Mostly interchange, then dissociative 7 coordinate of associative is unlikely
31
What is an encounter pair
Reactants that have come into contact but have not yet successfully reacted
32
What is the rate equation of octahedral substitution
kobs[M]tot[ligand] kobs = kKE Only for when KE[ligand] << 1
33
What are the 2 main effects on octahedral reactions
Spectator ligands and steric effects
34
Explain effect of spectator ligands on octahedral reactions
sigma donors increase e density forcing weak ligand to dissociate sigma donation stabilises the reduced coordination transition state
35
Explain the steric effects on octahedral reactions
Big ligands either chiral or achiral, whatever one more sterically hindering will have a faster rate due to favouring dissociation to reduced hinderance increased cone angle = increased rate
36
If 2 ligands are sterically the same but the rate is different...
likely due to electronic properties
37
What is ligand field activation energy (LFAE)
LFAE =LFSE(ts) - LFSE Comes from change in geometry from octahedral to square pyramidal or trigonal bipyramidal
38
Discuss radius and electron density on octahedral activation
decreased radius and increased electron density make it hard for nucleophilic attack. Therefore harder for nucleophilic attack going from 3d3 to 3d8
39
Discuss the stereochemistry of octahedral substitution
cis reactant goes through square pyramidal and produces cis trans goes through trigonal bipyramidal and produces cis or trans stronger pi donor equatorial and trans favours isomerisation
40
Discuss the D-CB mechanism
Base hydrolysis, replacement of ligand by OH-, overall a proton transfer Deprotonation decreases charge which increases lability OH takes proton from attached ligand. Forms H2O Weak ligand dissociates H2O replaces ligand and H is given back to initial ligand
41
Outline an inner sphere mechanism
electron and ligand transfer by forming bridge one reactant is labile (e donor) other reactant has bridging ligand reactants are not too bulky (therefore not biological reactions)
42
Outline an outer sphere mechanism
e transfer by forming encounter pair increased charge = small bond length = stretches decreased charge = long bond length =compresses Lengths distort to halfway between bond lengths
43
What does a high and low Ea mean with respect to an outer sphere mechanism
High Ea = more different bond lengths, more distortion needs to occur Low Ea = similar bond lengths or already distorted (e.g. Jahn Teller)
44
How can bond length be determined by eg orbitals
eg orbitals are anti bonding, therefore more electrons means longer bond length t2g orbitals are non bonding therefore don't really affect bond length

eCHM3941 (6 decks)

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