Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CH20148 > 20148 key concepts > Flashcards

20148 key concepts Flashcards

1
Q

trend in co-ordination numbers down groups

A

wider range of coordination numbers for 2nd and 3rd row metals than for first row. For first row metals 4 and 6 are most common, with 6 rarely exceeded

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Metal-metal bonding more common for…

A

2nd and 3rd row metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Exceptions to TM 4s^2 rule

A

Cr and copper, both 4s^1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why is the 4s orbital usually occupied

A

3d orbital lower in energy but 4s orbital occupation means less e-e repulsion, which outweighs cost of occupying higher energy orbital

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why doesnt the 4s filling apply in a compound

A

orbitals large so less e-e repulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Maximum oxidation state for Sc–>Mn

A

corresponds to oxidation state with all 3d and 4s electrons removed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Maximum oxidation state for Fe–>Cu

A

difficult to attain, still contains d electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Trend in +2 vs +3 oxidation state in TMs- rationalise

A

+3 more common than +2 in earlier transition metals

Increasing IE across the series, and increasing core-like behaviour of d orbitals across the series.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

zero or negative oxidation state possible with which ligand

A

CO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

High oxidation states possible with which ligands

A

fluoride and oxide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Order of stabilisation in oxidation states for halides

A

F-> Cl-> Br-> I-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does reaction of V with halides (X2) give and why

A

VF5, VCl4 and VBr3

F best at stabilising so can maintain higher oxidation state of V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

+2 oxidation states

A

oxides and halides form binary compounds MO MX2

All first row TMs with the exception of Ti form [M(H2O)6]2+ in aqueous solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

+3 oxidation state

A

Formed for all TMs, but Cu3+ is very oxidising
[M(H2O)6]3+ known for Ti–> Co
[Ti(H2O)6]3+ and [V(H2O)6]3+ both oxidised by air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

+4 oxidation state

A

Most important oxidation state for Ti- these compounds have high covalent character and high charge density on the metal makes it very polarising

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

TiCl4

A

covalently bonded liquid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

TiCl2

A

ionic solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

More positive value of E°

A

greater strength of oxidising agent on LHS of equation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Powerful oxidising agents only observed with

A

oxide and fluoride ligands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

E° value from Latimer diagram

A

(n1 x E°1 + n2 x E°2) / (n1 + n2)

where n= number of electrons
1= reaction 1
2= reaction 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Frost diagram plots

A

nE° against oxidation state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How can you obtain E° from a Frost diagram

A

gradient of the line linking 2 oxidation states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

If an intermediate oxidation state lies above the line linking oxidation states, ….

A

the disproportionation reaction will be thermodynamically favourable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what does high pH favour in terms of oxidation states

A

higher oxidation states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Chromium, Molybdenum and Tungsten

A

CrO3 and [CrO4]2- strong oxidising agents
WO3 and [WO4]2- not readily reduced
OS: 1st row< <2nd row<3rd row

Mo(IV) and W(IV) very common, but Mo(III) and W(III) sparse
High co-ordination numbers possible eg [Mo(CN)7]5- pentagonal bipyramidal
Metal-Metal bonds more common for Mo and W than Cr
Most Mo(II) and W(II) compounds contain M-M bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Nickel, Palladium and Platinum

A

For Ni and Pd, +2 is the only important oxidation state in aqueous solution, but for Pt 4+ is also important
For Pd and Pt square planar is the most important geometry for +2
M-M bonds and low OS’s become more important down the group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Which approach can be used ton explain the SCS

A

LF theory, a MO based approach

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

4s orbital

A

a1g symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

4p orbital

A

t1u symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

3d orbitals (x2-y2 and dz2)

A

eg symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

3d orbitals (xy, xz and yz)

A

t2g symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Additional Pi bonding in Tm complexes from…

A

Filled p orbitals into d orbitals- filled p lying perpendicular and can interact with d orbital not involved in sigma bond, so interacts in a Pi manner
Empty Pi* orbitals into d orbitals- have right symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Draw the partial MO diagram for Pi donor ligands

A

Draw the partial MO diagram for Pi acceptor ligands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

How do Pi donor ligands effect delta oct

A

reduce it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Pi donors include

A

O2- and N3-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Pi acceptors include

A

CO,CN- and C2H4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Are ligands at the top of the SCS Pi donors or acceptors

A

acceptors (incr delta oct, greatest splitting energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Nephelauxetic effect

A

Pairing energies lower in metal complexes than in gaseous ions, because orbitals bigger and less electron-electron repulsion in complexes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

How do CO ligands co-ordinate to the metal centre

A

Through the less EN carbon atom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is backbonding (CO)

A

Pi donation from a filled d orbital on M into empty Pi* orbital on CO
Electron density going opposite direction to sigma donation (from filled orbital on CO to empty metal d orbital)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Greater degree of backbonding = lower/higher stretching frequency

A

lower

stronger bonds = higher frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Tolman cone angle

A

measure of ligand size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Phosphine ligands properties

A

P d orbitals acceptors, P-C sigma* orbitals act as acceptors

Tertiary phosphines good sigma donors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

structural role of TMs

A

stabilising protein structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

functional role of TMs

A

metal ion involved in reactivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

How many haem groups does Hb have

A

4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What is iron bound to in Hb and Mb to give a haem group

A

porphyrin ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

Mb function

A

storage of oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What happens when oxygen binds in deoxyhaemoglobin

A

Electron configuration changes high to low spin t2g4 eg2 to t2g6/5. Since antibonding eg orbitals are no longer occupied the ion is smaller, so can move into the haem ring/plane
Forms oxyhaemoglobin and oxygen co-ordinated in a bent-on manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Role of metal centre in electron transfer proteins

A

provide a reversible binding site for an electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Which is iron a good metal to use in electron transfer proteins

A

Its has 2 OS’s readily available: Fe2+ and Fe3+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

Ferrdoxins properties

A

iron-sulfur proteins, characterised by iron reduction potentials less than 0V. Ferredoxins contan 2,3, or 4 iron centres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Bacterial rubredoxins

A

contain only 1 iron centre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

cytochromes

A

iron-haem proteins. cytochromes have higher electrode potentials than ferredoxins

55
Q

cytochrome a

A

haem group contains a formyl group (CHO)

56
Q

cytochrome b

A

protein not covalently bonded to the haem

57
Q

cytochrome c

A

protein is covalently bonded to the haem

58
Q

cytochrome d

A

the haem is a dihydroporphyrin

59
Q

which cytochromes are 6 co-ordinate and low spin

A

b and c

60
Q

which cytochrome is 5 or 6 co-ordinate

A

a

61
Q

role of cytochrome c in ETC

A

transfers electrons from cytochrome c1 to cytochrome c oxidase. Since the iron is low spin, it can fit in the centre of the haem ring

62
Q

What is an oxidase

A

uses o2 as the electron acceptor

63
Q

Role of cytochrome c oxidase in the ETC

A

final step
contains 4 metal centres- two Cu and 2 Fe
couples electron transfer with proton pumping to catalyse the reaction:
O2 + 4H+ + 4e- –> 2H2O

One of the iron centres is a 5-co-ordinate cytochrome a that can irreversibly co-ordinate O2

64
Q

What is the toxicity of cyanide a result of

A

The irreversible co-ordination of CN- to cytochrome a, which shuts down electron transfer to oxygen

65
Q

Where in mammals is iron stored

A

liver, bone marrow and spleen in the form of ferritin

66
Q

What does ferretin consist of

A

a hollow protein, with a cavity of around 80 armstrongs

Each protein molecule contains up to 4500 high spin Fe3+ centres

67
Q

What happens to cis platin once inside a cell

A

hydrolysed to give an aqua compound. Labile water molecules then replaced with N atoms from 2 of the DNA bps

68
Q

lability

A

ease with which ligands are replaced

69
Q

Which base does the majority of cis platin bridge between

A

neighbouring guanine bases on the same strand of the double helix

70
Q

Effect of cis platin on DNA

A

The chelation tilts the guanine rings from their normal stacked position. This disrupts the helix and interferes with replication
causes the development of resistance in cancer cells

71
Q

Cis platin side effects

A

severely toxic, doses possible limited

Problems include kidney damage, nausea, hair loss and neurotoxicity.

72
Q

How is cis platin taken and how

A

orally because not soluble in water

73
Q

carboplatin

A

dicarboxylate less labile than chlorides- lower toxicity so larger doses possible

74
Q

satraplatin

A

Pt(IV) compound so more soluble

May be reduced to Pt(II) in vivo

75
Q

JM335

A

does not have cis amines- different mechanism?

76
Q

Thermodynamics

A

tells us about the extent of a reaction
Relates to Delta Go
Defined by equilibrium constant K
stable/unstable

77
Q

Kinetics

A

tells us about the speed of a reaction
Relates to delta G ++ (the activation energy)
quantified by rate constant k
inert/labile

78
Q

Why do stepwise fomation constants (K1,K2 and K3) decrease in the order K1>K2>K3

A

statistical argument

decreasing number of molecules in the complex, so the probability of substituting a molecule is reduced

79
Q

Equilibrium constant for full substitution of the ligands

A

Given by formation constant B

B6= K1 x K2 x K3 x K4 ……

80
Q

Why might there be a high value of B

A

Larger CFSE for complex with final ligands vs original (H2O)

81
Q

Chelate effect

A

complexes with chelating ligands have higher stability over complexes with monodentate ligands

82
Q

2 factors involved in the chelate effect

A

entropic increase in disorder, increase in number of molecules in the reaction left to right when chelate ligands co-ordinate
2nd is that once one end of a ligand is coordinated, less rearrangement is needed for the other end to coordinate as opposed to another ligand.

83
Q

Hard cation

A

high charge density, non-polarisable

84
Q

outer sphere ligands

A

second sphere of solvent molecules loosely associated

85
Q

Disassociative mechanism

A

2 step process
M-X bond broken, giving an intermediate of reduced coordination number. This intermediate reacts with Y to give the product

86
Q

Formula for metal complex and ligand

A

MLxX + Y

87
Q

What is disassociative reminiscent of

A

SN1

88
Q

Associative mechanism

A

2 step process
First step is M-Y bond formed
Gives intermediate of increased coordination number
This intermediate loses X to give the product

89
Q

Why is there no organic analogue of the associative mechanism

A

Carbon generally cant be 5 coordinate

90
Q

Interchange mechanism

A

1 step process

M-Y forms as M-X breaks

91
Q

What does the reaction profile in the interchange mechanism reflect

A

That theres no intermediate

92
Q

When is there associative activation (Ia)

A

When the metal is substantially bonded to X and Y during the migration

93
Q

When is there dis-associative activation (Id)

A

If migration of X is to the outer sphere is well advanced before Y begins to move to the inner sphere

94
Q

What do complexes with a d8 configuration often form

A

sq planar complexes, especially with a large delta oct (2nd and 3rd row metals)

95
Q

why has most of the kinetic work in square planar complexes used Pt(II)

A

inert to oxidation and reduction
almost always sq planar
rate of ligand substitution is slow so it is easy to study

96
Q

How does substitution normally occur for sq planar complexes

A

through associative mechanisms (A or Ia)

97
Q

Evidence for associative mechanisms

A
  1. rate constants for displacement of Cl by H2O Pt complexes with different overall charges are similar. This suggests an associative mechanism, since a disassociative pathway would be dependent on charge of the complex (charge is important eg splitting into 2 anions more favourable)
  2. these reactions occur with stereoretention ( ligands cis to X still cis to Y). vs in D, forms trigonal planar intermediate so all 3 ligands equivalent
  3. Reactions accompanied by large -ve delta S++
    signifies loss of molecular freedom approaching the transition state (crowded TS), intermediate more ordered than starting material
  4. If the pressure is increased, subs accelerated and large, negative volume of activation is observed
98
Q

negative entropy=

A

less disorder

99
Q

What is the 2 term rate law for the associative mechanism

A

(2nd order)

100
Q

How can you get pseudo 1st order conditions and what does the rate equation simplify to

A

Uses a vast excess of [Y}, so it is essentially unchanged in the reaction

101
Q

How can k1 and k2 be calculated

A

carrying out the reaction with different concentrations of [Y]

102
Q

How can you calculate k2 from a plot of [Y] against kobs

A

gradient

103
Q

what happens if kobs if plotted against [Y] for differing entering groups in the same solvent

A

a common intercept is observed

104
Q

how does the intercept change (kobs against [Y])

A

with solvent

105
Q

In polar solvents what dominates

A

k1

106
Q

What does the k1 pathway involve

A

Association of the solvent first, X leaves and then Y associates
Solvent leaves last

107
Q

What does the k2 pathway involve

A

Normal association mechanism, Y associates then X leaves

108
Q

Nucleophilicity sequence

A

Rate k2 decreases

studying effect of entering group on rate of substitution of [Y]

109
Q

Where are soft donors in the nucelophilicity sequence

A

high

110
Q

What does increasing steric bulk of the spectator ligands do

A

slows substitution

111
Q

When is the effect of steric bulk more dramatic

A

When the bulky ligand is cis to the leaving group, X

112
Q

What process is the bulky observation consistent with

A

associative,

113
Q

What does the bulky theory suggest

A

suggest route passes through tbp and not square pyramid
For a square pyramid there would be little difference between the cis and trans ligands
In tbp cis ligands in axial plane vs trans in equatorial plane, same as X and Y

114
Q

trans effect

A

effect of a ligand on the substitution rate for the ligand trans to it

115
Q

Ligands high in the trans effect series are

A

Most labilising

ligands trans to them come off much easier

116
Q

What is more important , trans electronic effects or cis electronic effects

A

trans electronic effects

117
Q

2 possible origins for decrease in activation energy

A

destabilisation of ground state

stabilisation of transition state

118
Q

What is the trans effect series a balance between

A

sigma and Pi effect

119
Q

the sigma effect as an origin of the trans effect

A

Destabilises ground state relative to the transition state
Trans ligand T and leaving group X compete for the same metal orbitals (dz^2 and pz) in the ground state. This competition is relaxed in the tbp TS

120
Q

Strong sigma donors give

A

strong trans effects ( ie high up in series)

121
Q

Pi effects as an origin of the trans effect

A

If trans ligand T is a pi acceptor, charge delocalisation eases formation of the 5 COODN TS/intermediate
Strong pi acceptor ligands accept the ED donated by the incoming nucelophile, which lowers E of TS

122
Q

Give examples of which ligands give strong trans effects through pi acceptance

A

Ligands such as CO and CN- give strong trans effects through this mechanism

123
Q

Trans influence

A

effect of ligand on ground state properties such as NMR and coupling constants

124
Q

Trans influence series can be regarded as

A

just sigma components of trans effects

Pi effects not important because no TS

125
Q

What do studies on octahedral complexes use and why

A

Cr3+ and Co 3+

complexes inert, so rates of reaction are slow enough to study

126
Q

The higher the charge, what happens to lability of ligands

A

less labile (same d electron count)

127
Q

Evidence for dissociative mechanisms

A
  1. Rates unaffected by nature of entering group
  2. Rate depends on nature of the leaving group
  3. rate of substitution increases with increasing M-X bond length
  4. Rates are increased by increasing bulk of spectator ligands- ie block entering ligand from access to metal centre so lower chance of associative mechanism ie ligand associating first
  5. Increasing pressure slows down the reaction (V++ is positive)
128
Q

acid catalysis requires

A

a lone pair for protonation, making a better leaving group

129
Q

2 types of electron transfer reaction

A

inner and outer sphere

inner involves forming a covalently bonded bridging ligand, outer does not

130
Q

Outer sphere electron transfer needs to overcome

A

electrostatic repulsion between ions of like charge

both complexes cationic- makes it hard for them to get close together and slows the reaction

131
Q

What needs to be formed in the outer sphere reaction

A

vibrationally excited states with equal bond lengths to allow electron transfer

132
Q

greater change in bond lengths in an outer sphere reaction..

A

slower the rate of electron transfer

133
Q

What does an inner sphere transfer mechanism involve

A

covalently bound bridging ligand which may or may not be transferred with the electron

134
Q

3 steps in inner sphere electron transfer reactions

A

bridge formation, electron transfer and bridge cleavage

CH20148 (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions