Colour Design Flashcards
What is the difference between the reactions of alkenes and benzene?
Alkenes tend to undergo electrophilic addition reactions where as benzene tend to undergo substitution.
Why do benzene undergo substitution reactions?
Because of the stable ring structure formed by delocalised electrons. It can maintain the delocalisation by replacing a hydrogen which aren’t involved with the delocalised electrons
What is an electrophile?
Electron deficient species that are attracted to an electron rich centre, reacting by accepting an electron pair in order to form a nucleophile.
What are some examples of electrophiles?
Hydronium ion, boron trifluoride, aluminium chloride and halogen molecules fluorine, chlorine, bromine and iodine
What is bromination?
An example of an electrophilic aromatic substitution reaction where the electrophile forms a sigma bond to the benzene ring before a proton is removed to form a substituted benzene ring
What is formed in bromination?
A benzene ring called bromobenzene
What are the conditions of bromination?
A catalyst of FeBr3 is needed to make the Br2 more electrophilic by polarising it
What is the role of the iron catalys?
To make the Br2 molecule more electrophilic
How is the iron catalyst in bromination different to traditional transition metal catalysts?
It gets permanently changed during the reaction to form iron (III) bromide.
What is the equation for the reaction between bromine and the iron catalyst?
2Fe + 3Br2 –> 2FeBr3
H+ + FeBr4- –> HBr +FeBr3
What is chlorination?
It is an electrophilic substitution reaction between chlorine and benzene
What is the product of chlorination?
A mixture of mono and dichlorobenzenes
What are the conditions for chlorination?
Room temp, in the presence of an aluminium catalyst (normally) and under anhydrous conditions
Why is chlorination done at room temp?
Due to the combination of reactive chlorine and powerful halogen carrier aluminium chloride
Why must chlorination occur under anhydrous conditions?
Because aluminium chloride reacts violently with water
What is the role of the aluminium catalyst in chlorination?
It acts as a Lewis Acid catalyst by enhancing the electrophilicity of chlorine, generating a more reactive electrophile.
What is the equation for the formation of the electrophile?
Cl2 + AlCl3 –> AlCl4- + Cl+
Why are halogenated benzene derivatives so important?
They have been found to be important intermediates in synthetic routes and the carbon atom attached to the halogen can attack other carbon atoms, allowing C-C bonds to form
What is alkylation?
Alkylation involves the substitution of an alkyl group onto a benzene ring by replacing a hydrogen with a group like methyl or ethyl ect.
What are the conditions for alkylation?
Benzene is reacted with chloroethane and anhydrous aluminium chloride under reflux
What is the role of AlCl3 in alkylation?
The AlCl3 acts as a catalyst and a reactant in the formation of the electrophile.
What is the equation for the formation of the electrophile in alkylation?
CH3CH2Cl + AlCl3 –> CH3CH2+ + AlCl4-
What is an acyl group?
an alkyl group attached to a C=O bond
What are the conditions for acylation?
Reacting with an acyl chloride (or acid anhydride) and aluminium chloride under anhydrous conditions
What is the equation for the formation of the electrophile in acylation?
CH3COCl +AlCl3 –> CH3CO+ + AlCl4-
Why are the Friedel-Crafts reactions so important?
They are able to transform simple aromatic compounds into more complex ones which is useful in the synthesis of medicines, dyes, polymers and other organic materials
What do arenes and aromatic compounds include?
A benzene ring
How does the Kekule model of benzene describe the length of the bonds?
There should be 3 bonds the length of a C-C bond and 3 bonds the length of a C=C bond
How did they discover the true length of the bonds within benzene?
Through x-rays diffraction studies, they discovered the C-C bonds are the same length
How does the delocalised model of benzene explain benzene’s properties?
The carbons are arranged within a ring, but there are no alternating single, double bonds and instead each carbon donates and electron form its p-orbital and the p-orbitals combine to form a ring of delocalised electrons
What kind of reaction does benzene undergo?
Substitution reaction- a hydrogen gets swapped with something else, keeping the stability of the delocalised electrons
Why is the ring within benzene stable?
The electrons have more room to spread out than if they were in localised double bonds meaning they can get further away from one another, spreading out the negative charge to become more stable.
What would you expect the enthalpy change of benzene to be if the Kekule model was correct?
You would expect it to have an enthalpy change 3x that of a single C=C bond. However, it is only -208kJ mol-1
What type of reaction do arenes undergo?
Electrophilic Substitution
How do you make nitrobenzene?
Warm benzene with conc. nitric and sulfuric acid.
1.Sulfuric acid as a catalyst helps to make NO2+ which is an electrophile.
2. In order to only add one NO2 group, you need to keep the temperature between 55c
