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CHM2003M
REVISION
GUIDE

1

Table of Contents
1
...
Table of Contents
3
...
Physical T2- Homogeneous Catalysts
5
...
Physical T3- Enzyme Kinetics cont
...
Physical T4- Photochemistry
8
...
Physical Example Q/A
10
...
Inorganic T2- Organometallics basics
12
...
Inorganic T3- Organometallic reactions cont
...
Inorganic T4- Metallocene’s and M-M bonds
15
...
Inorganic Example Q/A
17
...
Organic T2- EDG/EWG in mechanisms
19
...
Organic T4- Synthesis and reactions of carbenes
21
...
Organic Example Q/A

2

Physical Chemistry T1- Kinetics of Complex
Reactions
Consider the simplest complex reaction: A→I→P
...
For each step, you can deduce a rate equation e
...

Step 1- A→I

where v1=k1[A] which is equal to −

Step 2- I→P

where v2=k2[I] which is equal to

•

𝑑[𝐴]
𝑑𝑡

𝑑[𝑃]
𝑑𝑡

For complex rate equations, we can combine the rate equations of elementary reactions to
form one for the overall reaction
...


•

However, intermediates cannot be included in rate laws
...


•

This is done by producing a differential equ
...
[I] is formed in s1
and removed in s2
...
of its rate of change would be:

•

𝑑[𝐼]
𝑑𝑡

= 𝑘1[𝐴] − 𝑘2[𝐼]
...
The SSA says
that the [I] remains constant and small throughout the reaction (except @ the very beg
...


•

Instead of integrating the differential equ
...
This is no longer differential
...


•

Now we can substitute this equ
...
v2 e
...


𝑑[𝑃]
=
𝑑𝑡

k2[I] is now

𝑑[𝑃]
𝑑𝑡

=

𝑘1

𝑘2 𝑘2 [𝐴]
...


Since only k1 and [A] are involved then this means that the reaction only depends on step 1
of the reaction
...
g
...


3

Physical Chemistry T2- Homogeneous Catalysts
Consider the reaction: 2H2O2 (l)→ 2H2O (l) + O2 (g)
...
Homogeneous catalysts are catalysts that are in the same state
(solid, liquid, or gas) as the reactants
...
This all begs the question, what
exactly is a catalyst and what does it do?

•

Catalysts accelerate a reaction but undergo no net chemical change themselves
...


•

In the presence of the catalyst the un-catalysed reaction still continues at its slower rate,
but the rate of formation of products is dominated by the rate of the catalysed reaction
path
...


•

In a catalytic cycle, C is consumed to form I which then reacts to form products and
regenerate the catalyst
...
The total conc of catalysts

A simple bi-molecular reaction: R1 + R2→ P
...


This reaction demonstrates a feature of homogeneous catalysts, which is that they are involved in the
rate equ
...
Therefore, the overall rate of
reaction would be equal to both the uncat and cat reactions e
...
Voverall=kuncat[R1][R2]+kcat[R1][R2][C]
...


remains constant e
...
[C]T= [C]+[I]
...

•

The resting state of the catalytic cycle is the catalytic species that has the highest conc
during the cycle
...
g
...


4

Physical Chemistry T3- Enzyme Kinetics
•

Enzyme catalysis is homogeneous

•

In enzyme catalysis, E binds to the substrate, S, to form an intermediate complex ES

•

At the active site, the types of interactions between E and S are non-covalent e
...
hydrogen
bonds

•

Reasons why the rate of reaction (ROR) increases with the introduction of an enzyme
catalyst includes: binding of the substrate brings molecules into close contact and effectively
increases their concentration, substrates are bound at the active site in a favourable
orientation, binding of S weakens bonds and facilitates formation of the active complex, the
formation of the active complex is stabilised by tight binding which lowers the activation
energy
...
Therefore, we can derive a rate
equation for this reaction using the SSA
...
g
...


•

We assume the rate of change of [ES]=

•

Overall, the SSA derived rate law is

•

Vmax is the maximum rate that would be observed when all of E is present as ES
...

𝑘1𝑘2[𝑆][𝐸]𝑇

= 𝑘1[𝑆]+𝑘−1+𝑘2
...
g
...


5

•

Above is an example of a Lineweaver-Burke reciprocal plot, which is how you linearise the
Michaelis-Menten rate laws
...

•

Problems with the L-B plot are: equally spaced increments of [S] do not give equally spaced
points on a reciprocal plot meaning points can become clustered and this messes with
determining the line of best fit, and small errors in rate are magnified on the reciprocal plot
which can give significant error to the slope
...


•

The turnover frequency, Kcat, is the number of catalytic cycles (turnovers) or the number of
substrate molecules transformed in one-unit time by a single enzyme molecule when the
enzyme concentration is rate-limiting
...


•

In competitive inhibition the inhibitor binds to free enzyme molecules thus preventing them
from substrate binding
...
In classic competitive inhibition, the inhibitor and the substrate directly
compete for a single binding site
...


•

The effect that competitive inhibition has on the νmax and km is that νmax appears to be
unaltered and km appears to increase
...
)

•

In uncompetitive inhibition, the inhibitor does not bind to the free enzyme an instead
irreversibly binds to the ES
...
(y-intercept increases, slope is
constant)

•

Non-competitive inhibition is also called mixed inhibition
...


•

I has no effect on S binding
...


•

Vmax decreases and Km is unchanged
...


6

Physical Chemistry T4- Photochemistry
Laws of Photochemistry:
1
...

2
...
Only the light which is absorbed by the substance can bring about photochemical change
...
If some or all of the light particles can be absorbed by the sample, then the
transmitted light intensity (It) will be lower than the initial intensity (I0) of the light
...


•

The Beer-Lambert law says the intensity of light decreases exponentially with the
concentration of the absorbing species and the path length
...


•

Absorbance can be obtained through A=logI0/It
...


•

A triplet state means that an electron is promoted with a spin state parallel to the electron
in the orbital that it was previously in, a triplet state is usually lower in energy than a singlet
state as repulsion between electrons is lower
...


•

Internal conversion is going from Sn→S1 and/or S1→S0

•

Intersystem crossing is going from S1→ T1 and then T1→ S0

•

Fluorescence is going from S1→S0+hv

•

Phosphorescence is going from T1→ S0+hv

•

A substance that accelerates the decay of an electronically excited state to a lower state is a
quencher (Q) and is said to quench the excited state
...
Calculate KM
...
The enzyme-catalysed conversion of a substrate at 25oC has a Michaelis constant of 8
...
The rate of reaction is 12
...
75 x 10-2 mol dm-3
...
6𝑥10−6 (8
...
75𝑥10−2 ])
[1
...
84x10-5 mol2 dm-6 s-1
...
54 × 1011 ! Try the calculation catalase (Ea = +8 kJ mol-1 uncatalysed
(E ) a = +75 kJ mol-1)

A3) Assume that the pre-exponential factor, A is the same e
...
𝑘r(catalase) = 𝐴𝑒−8000 𝐽 𝑚ol−1/ (8
...


A x 3
...
For the uncatalyzed reaction, 𝑘r(uncatalysed) = 𝐴𝑒−75000 𝐽 𝑚ol−1/ (8
...
A x 7
...
Then you just divide the catalysed reaction by the uncatalyzed reaction e
...

𝑘𝑟(𝑐𝑎𝑡𝑎𝑙𝑎𝑠𝑒)
𝐴 𝑥 3
...
54𝑥1011
𝑘𝑟(𝑢𝑛𝑐𝑎𝑡)
𝐴 𝑥 7
...


9

Inorganic Chemistry T1-E- Counting and Ligand
Types
In terms of binding, ligands can be classified into pi-donor, sigma-only, and pi-acceptor ligands
...


•

Sigma only/ sigma donor ligands donate electrons to the metal orbitals via a sigma bond
...


•

The 18-electron rule states that thermodynamically stable transition metal complexes
contain 18 valence electrons, comprising of the metal’s d-electrons plus the electrons
supplied by the metal bound ligands
...
These two ways are the
neutral and ionic methods
...


•

In this method, we consider the metal centre and all of the ligands to be neutral
...
Ligands that contribute 2e- and those that contribute 1e-
...
g
...


•

Due to the lanthanide contraction, the radii of the 2nd and 3rd row transition metals are very
similar
...


•

Earlier metals (G4-7) exhibit the widest range in oxidation states with higher oxidation
states being observed for 2nd and 3rd row metals
...

This means that the bonding in these 3d metals can be described as covalent
...
This means that the bonding in these metals is considered
almost completely ionic
...


•

U= the number of metal atoms bridged by a ligand
...


o

For compounds that consist of one or more ions, the cation is named first and then
the anion

o

Ligands are named first in alphabetical order, then the metal is named with its
oxidation state in brackets, then the suffix ‘-ate’ is added if the complex is anionic
...


o

For neutral ligands, the common name of the molecule should be used e
...
aqua for
H2O, ammine for NH3, carbonyl for CO, and dinitrogen/dioxygen for N2/O2
...
g
...
This is also for if the ligand is a polydentate ligand
...


o

E
...
[Cr(NH3)3(H2O)3]Cl3 when named is= triamminetriaquachromium(III) chloride

11

Inorganic Chemistry T3-Organometallic reactions
Reaction 1- CO substitution: Happens thermally or photochemically
...
E
...
Fe(CO)5 + P(CH3)3 → Fe(CO)4(P(CH3)3) +
CO
...
The loss of CO from the 18 e- complex is slow, but the addition of
the new ligand to the 16 e- intermediate is fast
...
The metal must start in a low oxidation state and have an accessible higher oxidation
state
...
E
...
LnM + X-Y → LnMXY
Oxidative addition initially gives a cis-addition product, but ligand rearrangements can occur, and the
isolated product may include the groups mutually cis or trans
...
The metal must start in a high (ish)
oxidation state and have an available lower oxidation state
...
g
...
During
RE, the e- in the M-R bond go to the R ligand, and the M-R’ e- go to the metal
...


Reaction 4- Migratory insertion: In migratory insertion, there is an anionic ligand (Y) and a neutral
unsaturated ligand (X) in cis positions
...
This produces a vacancy at the metal, meaning a coordination
site at the metal which is not occupied by a ligand
...
g
...
Metal alkyls that
contain β-hydrogens experience rapid elimination of these hydrogens with the right conditions
...
The product of a
migratory insertion reaction is stabilised by an agnostic M-H-C 3-center 2-electron interaction
...
) Because of the agnostic M-H-C interaction, β-hydride elimination is very fast
...
This is usually an irreversible reaction due to kinetic and thermodynamic
reasons
...


LnPdRX

+ LnMR’

LnPdRR’

+

LnMX

Reaction 7-Alkene metathesis: alkene metathesis (olefin metathesis) allows for the exchange of
substituents between different alkenes
...
Overall reaction (detailed reaction is a catalytic cycle) is shown below:

Catalytic processes to be aware of- 1
...


2
...


3
...

4
...


13

Inorganic Chemistry T4-Metallocene’s and
M-M bonds
•

Cyclopentadienyl moiety (Cp) ligands form a wide array of organometallic compounds with
metal atoms
...


•

Generic metallocene type complexes are formed for many of the 1st row transition metals
(Sc-Zn)
...


•

The bonding model requires a consideration of the overlap of metal orbitals with the pimolecular orbitals of the Cp
...


•

Some metallocenes have non-18 electron counts
...


•

In electron-deficient complexes, the addition of electrons achieves an 18-e- complex
(reduction to anion, addition of extra ligands)

•

In electron-rich complexes, the loss of electrons achieves 18-e- configuration (oxidation to
cation, derivatisation of Cp to change the number of e- it donates to the metal
...


•

Delta bonds are generally weaker due to poor overlap
...


•

A 3c-2e bond is a n electron-deficient bond where 3 atoms share 2 e-
...

The 2 e- go into the bonding MO
...


A1) 18 electrons fill 5d, 1s, and 3p orbitals, which is a stable noble gas configuration
...
Explain why the bonding in such species is often
termed synergic
...
There is sigma donor
interaction from the CO ligands, which increases the electron density on the metal by electron donation
from the CO HOMO to an empty d orbital on the metal and decreases the electron density on the CO
ligand
...
This bonding between M→ CO is often termed synergic as the sigma donor and pi
acceptor interactions reinforce each other
...
Explain how this complex can be in a non-18 electron configuration
...
These are usually early
transition metals and the ligands are usually pi-donors
...
g
...


Q4) The 1H NMR spectra of Fe2(CO)4(η5-C5H5)2 measured at T = -44 °C consists of one signal, and at T = 66 °C consists of two signals
...
Suggest a plausible explanation for the observed 1H
NMR results
...
At -44oC, the interconverting is too fast to distinguish in the NMR
...
The terminal and
bridge COs are existing in both cis and trans isomers, which can always be seen in IR
...


16

Organic Chemistry T1-Radical generation and
reactions
•

Radicals are neutral reactive intermediates that contain unpaired electrons
...
The e- is in the SOMO of the frontier orbitals
...
They get thermodynamic stability through the inductive effect,
hybridisation (sp3 most stable), and polarisation
...
It is the symmetrical homolytic
cleavage of a covalent bond to form 2 radical species
...


•

Propagation is the reaction of a radical with a closed-shell molecule
...


•

Termination is the destruction of radicals
...
This can happen from
photolysis or thermolysis
...


•

Propagation is exothermic
...
It is an exothermic process
...


•

SET oxidation reactions: consider the reaction above
...


•

SET reduction e
...
Birch reduction (benzene ring reduced to diene)
...


•

EWG= electron withdrawing group
...
They remove
electron density from the pi system and make it less nucleophilic
...
EWG can be recognised by either the atom adjacent to the pi
system having several bonds to more electronegative atoms or having a formal positive or
partial positive charge
...
In general, an EDG makes the ortho and para positions delta
negative
...
EDG can
be recognised by lone pairs on the atom adjacent to the pi system
...

X (Cl, Br, I)
CHO
CRO
COOH
COCl
+NH3
ONR2
NH2
OH

EWG
EWG
EWG
EWG
EWG
EWG
EDG
EDG
EDG
EDG

•

A Grignard reaction involves an organomagnesium compound reacting with a carbonyl
...


18

Organic Chemistry T3-Pericyclic Reactions
•

Standard reactions have intermediates whereas pericyclic reactions do not
...
This means your product has to be lower in energy than your starting material
...


•

The Diels-Alder reaction is an example of a cycloaddition
...


•

The resonance stabilisation of a positive charge will decrease the energy of the
HOMO+LUMO
...


•

The diene must have an s-cis conformation
...


•

A sigmatropic rearrangement is a reaction in which a sigma bonded atom or group that
is flanked by one or more pi electron systems shifts to a new location, with a
corresponding rearrangement if the pi bonds
...


•

Another consequence of pericyclic reactions is that there is a decrease in the entropy
...


19

Organic Chemistry T4-Synthesis and Reactions of
Carbenes
•

A carbene is a neutral species containing a carbon atom with only 6 valence electrons
...


•

The bond angle of a singlet carbene is ~100-110, and in a triplet carbene it is ~130-150
...


•

Some typical carbene reactions are insertion into an OH bond, insertion into a C=C bond, or
insertion into a C-H bond
...


•

Carbenes are also used in alkene metathesis
...


A1)

Q2)

A2) Reaction a is an electrocyclic reaction with the single bond at the end shifting to make the top right
double bond etc
...
Lastly, reaction c is a electrocyclic reaction
...

22



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