Colour by Design

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  • Created by: Sabina
  • Created on: 07-04-16 14:19
What are arenes?
Aromatic compounds containing a benzene ring
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What was Kekule's structure?
Kekule suggested that the single and double bonds in a planar ring continuously alternated between the carbons
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How was Kekule's structure disproved?
There should be three bonds with the C-C bond length and three with the C double bond C length. However when x-rayed it was shown that all bonds had the same length.Also did not react with bromine,doesn't undergo electrophilic addition
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What is the delocalised structure?
Within a planar ring there is a ring of delocalised electrons. The carbons still arranged in a ring but no alternating single and double bonds. Instead each carbon donates an electron from its p-orbital which form a ring of delocalised electrons
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What type of reaction does a benzene ring undergo?
electrophilic substitution
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What happens if you add bromine to benzene
Nothing
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What are functional group does a fatty acid contain?
Carboxylic acid and alkene if it is unsaturated
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What are triglycerides?
Triesters of glycerol and fatty acids
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What type of reaction do 3x fatty acids and glycerol undergo to form a triglyceride?
Condensation/esterification
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Why does benzene react by substitution but not addition?
Electrons in a benzene ring spread out the negative charge so that the molecule is more stable. Addition would need to remove electrons from the stable ring to form new bonds, substitution just swaps H for something else preserving stable ring
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Give the reagents and conditions of nitration
Reagents:Concentrated nitric and sulphuric acid Conditions: Temperature below 55 degrees
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What is produced by nitration?
Nitrobenzene and H+ which reacts with HSO4- to reform the catalyst back into sulphuric acid
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What acts are the electrophile in nitration?
Nitronium ion (NO2^+)
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What does concentrated sulphuric acid do during nitration?
Acts as a catalyst
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What happens if the temperature exceeds 55 degrees in nitration?
You will get more than one nitro group substituted into the benzene ring
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Why won’t you get much trinitrobenzene formed?
NO2 groups make the ring much less reactive than benzene itself. By the time you get two NO2 groups attached, the ring is so unreactive that getting a third one attached is very slow.
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The nitration of methylbenzene happens about 25 times faster than the nitration of benzene. Explain why.
Methyl groups “push” electrons away from themselves towards the ring, increasing the electron density in the ring. That makes it much more attractive to the sort of things which the ring reacts with.
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Give the reagents and conditions of sulfonation
Reagents:Concentrated sulphuric acid or fuming sulphuric acid Conditions:Reflux or 40 degrees
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What is produced by sulfonation?
Benzenesulfonic acid
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What is the electrophile in sulfonation?
Sulfur trioxide (SO3)
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Why is sulfur trioxide an electrophile?
It is a highly polar molecule. The sulfur atom has a partially positive charge causing it to be attracted to the ring of electrons
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Where does the sulfur trioxide come from in sulfonation?
Conc. sulfuric acid is dissociated into sulfur trioxide and water. Fuming sulfuric acid is a solution of lots of sulfur trioxide molecules dissolved in sulfuric acid
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What is dissociation?
The reversible splitting up of a compound
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What are alkyl groups?
A group that has one few H than an alkane group
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What is an acyl group?
An alkyl group attached to C-O double bond
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What are the reagents and conditions of Friedel-Crafts acylation?
Reagent:Aluminium Chloride Conditions:Reflux
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What is the electrophile in Friedel-Crafts acylation?
Acylium ion
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How is an acylium ion formed in Friedel-Crafts acylation?
Formed by the reaction between the acyl chloride and aluminium chloride catalyst
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What is produced from Friedel-Crafts acylation?
Phenyketone, HCl and aluminium chloride
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What are the reagents and conditions of Friedel-Crafts alkylation?
Reagents: Aluminium chloride Conditions:Reflux
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What is a carbocation?
An organic ion with a positively charged carbon atom
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What is the electrophile in Friedel-Crafts alkylation?
carbocation
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How is the carbocation formed in Friedel-Crafts alkylation?
Reaction between chloroalkane and aluminium chloride
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What is produced from Friedel-Crafts alkylation?
Alkyl benzene e.g. methylbenzene, HCl and aluminium
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Reagents and conditions of halogention
Reagent:Aluminium chloride or iron Conditions:room temperature
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What is the electrophile in halogenation?
Partially positive end of halogen molecule
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How does iron become a catalyst in halogenation?
Reacts with bromine or chlorine to form iron(III) chloride or iron(III) bromide
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What is produced by halogenation?
Bromobenzene or chlorobenzene, HBr or HCl
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When will benzene undergo an addition reaction with chlorine or bromine?
In the presence of UV. Ring of delocalised electrons is permanently broken and Cl or Br is added on to each carbon atom
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Why are electrophilic substitution reactions of benzene relatively slow?
It needs quite a lot of energy to break the delocalisation on the ring and form the intermediate ion. That means that the activation energy for the overall reaction is high, and so relatively few particles will have enough energy to react
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What are aromatic amines used to make?
Azo dyes
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What are azo dyes?
man-made dyes that contain the azo group (-N double bond N-). This azo group is usually used to link two aromatic compunds
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How is an azo dye made?
First a diazonium salt is made. The diazonium salt is then coupled with an aromatic compound that is susceptible to an electrophilic attack e.g. phenol
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How is a diazonium salt formed?
Sodium nitrate and hydrochloric acid are reacted together to form nitrous acid. Nitrous acid is then reacted with phenylamine and HCl to form benzenediazonium chloride. Temperature must be below 10 degrees
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Describe the process of coupling benzenediazonium chloride with a pheno
Phenol is dissolved in a sodium hydroxide solution to make a sodium phenoxide solution.Cool solutution then add benzenediazonium chloride added.Azo dye precipitates out of the solution immediately
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Why is phenol a coupling agent?
The lone pairs on its oxygen increase the electron density of the benzene ring making it easier for the diazonium ion which is a weak electrophile to bond to it.
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What are the most permanent types of dyes
Dyes that have a functional group that will react with -OH of -NH in the fibre, forming strong covalent bonds.
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What is a chromophore?
A part of an organic molecule that causes it to be coloured
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How does a chromophore give an azo dye its colour?
Azo compounds contain highly delocalised system of electrons. If light falls on the molecule some wavelengths are absorbed by the delocalised electrons,which the chromophore is part of. The colour seen is complimentary to frequency of colour absorbed
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What will happen if a chromophore is modifyed?
Will cause a change in the frequency of light absorbed thus changing the colour of the molecule
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What can be done to adjust the colour of the dye molecule?Why?
Add functional groups containing O or N atoms with lone pairs of electrons. This is added as the lone pair of electrons becomes part of the delocalised system responsible for absorbing light
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What happens when an acid is added to methyl orange?
A hydrogen ion is gained causing it to become red
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What happens if an alkali is added to methyl orange?
A hydrogen ion is lost causing it to become yellow
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How is the solubility of a dye in water increased?
Ionic groups are added to the dye molecule these are often ionic groups e.g. sulfate ion. Water dissolves the ionic substances due to its polar nature
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Name two binding mediums
Oil and water
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Describe gas-liquid chromotography
Sample injected into stream of carrier gas which carries it through the tube to the stationary phase.Mixture dissolves in stationary phase, evaporates in mobile phase and redissolves in tube. Solubility determines how long in stationary phase
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What gas is used as the mobile phase in GLC?
unreactive gas e.g. nitrogen or helium
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What is retention time?
The time taken to reach the detector
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What does the area under the peak in GLC show?
The relative amount of each substance in the original mixture
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What can GLC be combines with to make it a better analytical tool?
Mass spectroscopy
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What happens if GLC is combines with mass spectroscopy?
Sample is separated by GLC. The separated components then go into a mass spectrometer. The spectrometer produces a mass spec for each component which can then be identified
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Describe how visible absorption spectrum is produced
Beam of monochromatic light is passed through a dilute solution of the pigment.A detector measures the amount of light absorbed by pigment. Different frequencies of light passed through solution showing which colour absorbed most strongly
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When is visible absorption spectroscopy used?
If you have a dilute solution of the pigment
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When is a visible reflection spectroscopy used?
If you are not able to make a solution of the pigment
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Describe how a visible reflection spectrum is produced
A beam of monochromatic light is shone onto the surface of a solid. The reflectance is measured. By changing the frequency of light and calculating reflectance a visible spectrum is produced
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Describe how an atomic emission is produced
High-energy pulse of light focused onto a tiny sample of paint causing pigment to vapourise.Vapour passed between two electrodes.Energy excites electrons in pigment->return to ground state->emit light with specific frequency.
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What is an electrophile?
Molecule with a partially positive charge that accepts a pair of electrons.
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Describe the arrangement of delocalised electrons in a benzene ring.
Two rings one is above the carbon atoms and one is below
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Card 2

Front

What was Kekule's structure?

Back

Kekule suggested that the single and double bonds in a planar ring continuously alternated between the carbons

Card 3

Front

How was Kekule's structure disproved?

Back

Preview of the front of card 3

Card 4

Front

What is the delocalised structure?

Back

Preview of the front of card 4

Card 5

Front

What type of reaction does a benzene ring undergo?

Back

Preview of the front of card 5
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