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F335 Chemistry by Design: Colour by Design
These intermolecular forces are the weakest .
Permanent dipole The + and charges on polar molecules cause weak electrostatic forces of
­ permanent attraction between molecules, e.g. HCl (H is + and chlorine is ).
dipole These intermolecular forces are stronger than instantaneous dipole induced dipole.…read more

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F335 Chemistry by Design: Colour by Design
(ii) describe the delocalisation of electrons in these compounds
(iii) explain how delocalisation accounts for their characteristic properties [limited to undergoing
substitution (often slowly) rather than addition reactions]
Benzene undergoes substitution rather than addition reactions with electrophiles. By reacting in this way, the
stable benzene ring system is kept intact. The reactions are relatively slow because the first step in the reaction
mechanism disrupts the delocalised electron system , and this requires a substantial input of energy .…read more

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F335 Chemistry by Design: Colour by Design
Organic Reactions
(g) describe and explain the following electrophilic substitution reactions of arenes, naming the benzene
derivatives formed:
Type of Reagents and Reaction
Electrophilic Conditions
Substitution
Halogenation ­ Bromination ­ Br 2(l) 1. The benzene molecule becomes polarised as it approaches the
bromobenzene and a halogen benzene ring.
, carrier, e.g. FeBr 3 2. FeBr 3 accepts a lone pair
chlorobenzene Room temperature. from one of the bromine
atoms, forming Br+ and
FeBr 4 .
3.…read more

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F335 Chemistry by Design: Colour by Design
Heat under reflux
with dry either.
(h) describe and explain the formation of diazonium compounds and coupling reactions that these undergo
to form azo dyes
Azo compounds contain the ­N=N­ group. Compounds in which the R groups are arenes are
much more stable than those with alkyl R groups. This is because the ­N=N­ group is
stabilised by becoming part of an extended delocalised system involving arenes.…read more

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F335 Chemistry by Design: Colour by Design
The oxygen in phenol and nitrogen in amine has lone pairs which increases the electron density of the benzene
ring ­ this gives the diazonium ion (weak electrophile) something to attack and be attracted to. Many different
azo compounds can be formed by coupling different diazonium salts with a whole range of coupling agents. Unlike
diazonium salts, the azo compounds are stable so their colours do not fade .…read more

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F335 Chemistry by Design: Colour by Design
(k) describe and explain the general principles of gasliquid chromatography:
(l) understand the techniques used to identify the materials used in a painting, including:
(i) gasliquid chromatography
(ii) atomic emission spectroscopy
(iii) visible spectroscopy (reflection and absorption)
and explain and predict given results from these techniques
Gasliquid 1. The stationary phase is a high boiling point liquid held on a
Chromatography finely divided inert solid support. The mobile phase is an
unreactive carrier gas (e.g. nitrogen, helium).
2.…read more

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F335 Chemistry by Design: Colour by Design
that lots of light is being absorbed . Therefore, the peaks of the
graph indicates the colour of the object.
Differences between Visible Infrared Spectra:
Vis peaks rise from the base line ­ shows radiation absorbed .
IR peaks hang down from base line ­ shows radiation transmitted .
Vis ­ wavelength (nm) .
IR ­ wavelength 1/ (cm1
).
Vis ­ gives broad absorption bands which are characteristic of general structural features rather than
individual functional groups.…read more

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