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eCHM3941 > INORGANIC SUBSTITUTION > Flashcards

INORGANIC SUBSTITUTION Flashcards

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…

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

A

Pseudo first order

kobs[metal]

kobs = k1 + k2[ligand]

20
Q

What is a nucleophilicity parameter

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

A

small radii

high positive charge

high energy LUMOs

22
Q

What are the characteristics of a hard lewis base

A

small radii

high electronegativity

high energy HOMOs

23
Q

What are the characteristics of a soft lewis acid

A

large radii

low positive charge

low energy LUMOs

24
Q

What are the characteristics of a soft lewis base

A

large radii

moderate electronegativity

low energy HOMOs

25
Q

What are the 3 factors on a square planar reaction

A

nucleophilicity of entering group

trans effect

steric effects

26
Q

Explain the trans effect

A

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
Q

Explain the steric effects on a square planar reaction

A

steric crowding blocks nucleophiles

therefore, inhibits associative mechanism and favours dissociative mechanism.

Sterics on trans to substitution site is better than cis

28
Q

Explain the stereochemistry of a square planar substitution

A

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
Q

What sign of S and V show associative mechanism

A

negative

30
Q

What are the most common mechanism of octahedral substitution and why

A

Mostly interchange, then dissociative

7 coordinate of associative is unlikely

31
Q

What is an encounter pair

A

Reactants that have come into contact but have not yet successfully reacted

32
Q

What is the rate equation of octahedral substitution

A

kobs[M]tot[ligand]

kobs = kKE

Only for when KE[ligand] &laquo_space;1

33
Q

What are the 2 main effects on octahedral reactions

A

Spectator ligands and steric effects

34
Q

Explain effect of spectator ligands on octahedral reactions

A

sigma donors increase e density forcing weak ligand to dissociate

sigma donation stabilises the reduced coordination transition state

35
Q

Explain the steric effects on octahedral reactions

A

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
Q

If 2 ligands are sterically the same but the rate is different…

A

likely due to electronic properties

37
Q

What is ligand field activation energy (LFAE)

A

LFAE =LFSE(ts) - LFSE

Comes from change in geometry from octahedral to square pyramidal or trigonal bipyramidal

38
Q

Discuss radius and electron density on octahedral activation

A

decreased radius and increased electron density make it hard for nucleophilic attack.

Therefore harder for nucleophilic attack going from 3d3 to 3d8

39
Q

Discuss the stereochemistry of octahedral substitution

A

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
Q

Discuss the D-CB mechanism

A

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
Q

Outline an inner sphere mechanism

A

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
Q

Outline an outer sphere mechanism

A

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
Q

What does a high and low Ea mean with respect to an outer sphere mechanism

A

High Ea = more different bond lengths, more distortion needs to occur

Low Ea = similar bond lengths or already distorted (e.g. Jahn Teller)

44
Q

How can bond length be determined by eg orbitals

A

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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