Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Georgina O’Malley

Colour by Design
Explain the origins of colour in transition metal complexes

Where ligands surround a transition metal, the 5 orbitals in the D subshell are split into 3 at
a slightly lower energy and 2 at a higher energy
...

The frequency of this photon absorbed determines the colour which is seen (if the light is in
the visible spectrum) as E=hv
...

Explain the origins of colour and UV absorption in organic molecules

A chromophore is a group which is part of an extended delocalised electron system e
...

benzene
...

Double bonds have a greater spread of electrons which require less energy to excite than
single bonds – this means they absorb photons in the visible spectrum
...

The alkalinity/acidity of the solution can also influence the colour of organic compounds, for
example the addition of an H+ group can change the frequency of photons absorbed in the
visible spectrum – thus changing the colour
...

Many are esters of the molecule propane-1,2,3-triol 
The 3 alcohol groups on glycerol allow it to react with 3 carboxylic acids to form 3
ester bonds (in a condensation reaction)
...


Georgina O’Malley

The carboxylic acids which react with glycerol are unbranched hydrocarbon chains with
even numbers of carbons
...

Oils/fats can be split using hydrolysis – the conditions are heating with concentrated sodium
hydroxide solution
...


The more unsaturated an oil is – the more double bonds it has – the more disrupted the
chains are – the greater the distance between chains – the weaker the intermolecular bonds
– the less energy required to break them – the lower the melting point
...

Describe and explain the general principles of gas-liquid chromatography

-

Sample is injected into inert carrier gas stream (nitrogen, the mobile phase)
A non-volatile liquid coats a finely divided solid (stationary phase) in the long, coiled
column
More volatile liquids will favour the gas phase and therefore emerge faster than
those favouring the stationary phase
Time taken to leave the column is recorded (retention time)
Retention times can be used to distinguish compounds (based on previous records)
Understand the techniques used to identify the materials used in a painting

Gas liquid (see above)
Atomic emission spectroscopy:
Laser microspectral analysis produces an emission spectrum for the pigments, the frequency
of light emitted is proportional the gap in energy between levels (E=hv)
Visible spectroscopy:
(Absorption) Sample of paint dissolved in solvent and visible/UV light shone through this
and a sample of just solvent
...


Georgina O’Malley

(Reflectance) White light is shone on the paint and the light reflected is measured for
remaining wavelength of light
...

Recognise arenes and their derivatives (aromatic compounds)

An arene is an aromatic hydrocarbon – for example a benzene ring (C6H6)
Benzene, when displayed in the kelkulé structure, appears to have 3 unsaturated double
bonds in a set place
...


There are 3 pieces of evidence which support this ringed structure and contradict kelkulé’s
structure:






X-ray diffraction studies have produced electron density maps which show an even
distribution of electrons around each carbon – kelkulé’s structure would suggest
electrons are more densely concentrated between the 3 double bonds
The enthalpy change for the hydrogenation of benzene is much lower than would be
expected of 3 double bonds – implying that benzene is more stable than kelkulé’s
structure suggests
Bond lengths between the ‘double bonds’ in benzene are shorter than single bonds
but longer than alkene double bonds – this suggests that benzene does not have 3
double and 3 single bonds, rather 6 different bonds entirely

Benzene, having regions of high electron density is often attacked by electrophiles
...


Georgina O’Malley

Reactions with benzene are also slow, because large energy inputs are required to first
disrupt the ring
...
HNO3, benzene

Anhydrous iron (III) bromide,
room temperature
Conc
...
H2SO4, benzene

Friedel-Crafts Alkylation

Halogenoalkane,
benzene
Acylchloride, benzene

Heat under reflux for several
hours
Anhydrous AlCl3, heat under
reflux
Anhydrous AlCl3, heat under
reflux

Benzenesulphonic acid +
2H2O
R-group benzene e
...

methylbenzene + HCl
Phenyl R-anone (ketone)
e
...
phenylethanone

Friedel-Crafts Acylation

Nitrobenzene + H2O

Example mechanism (acylation):

Describe and explain the formation of diazonium compounds and coupling reactions that undergo to form
azo dyes

Diazonium ions are formed in the reaction of a phenylamine with acidified nitrous acid at
temperatures lower than 5°C
...
This produces an
N=N bond and is known as a coupling reaction
...

When reacting with a phenol:
The phenol is dissolved in sodium hydroxide solution to produce a sodium phenoxide ion

The solution is then cooled to below 5°C and the diazonium ion solution – a coloured
precipitate should be formed
...


The reaction with nathalen-2-ol occurs in exactly the same conditions
...


Describe and explain the structure of a dye molecule in terms of the chromophore

OH, SO3-Na+, NH2 and NR2

Georgina O’Malley

The presence of the sulphur trioxide in a sodium salt increases the solubility of the dye in
water
...

The addition of OH, NH2 or NR2 changes the colour of the dye by adding a lone pair of
electrons to the delocalised system, changing the frequency of light from which electrons
absorb energy to become excited
...

Direct dyes are a solution applied directly to the fibres – these undergo hydrogen and ID-ID
bonding
...




---