Aromatic Flashcards
Describe the bonding in benzene
Each carbon is covalently bonded to 2C’s and 1 H
Each C atom has 1 unbonded e- in its p orbital
P orbitals overlap to give a ring of delocalisation above and below the plane
This ring gives it stability
What gives benzene stability
Each C atom has 1 unbonded e- in its p orbital
P orbitals overlap to give a ring of delocalisation above and below the plane
This ring gives it stability
Where does the ring of delocalisation lie
Above AND below the plane
Describe the shape of benzene
Trigonal planar arrangement around each carbon giving a bond angle of 120 degrees
Therefore benzene is planar
Describe the bond length in benzene
Intermediate between single and double bond
Draw the both structures of benzene
Write the equation for the hydrogenation of cyclohexene stating the enthalpy change for the reaction
Write the equation for the hydrogenation of cyclohexa-1,4-diene and cyclohexan-1,3-diene, for both isomers, stating the enthalpy change for each reaction
Explain why the enthalpy change for the hydrogenation of cyclohexa-1,4-diene and cyclohexan-1,3-diene are different
C=C bonds in 1,4 diene are too far apart to allow overlap of p orbitals, so there is no additional delocalisation and no additional stability
In 1,3 diene, a section of the molecule is alternating, double single double bond. This allows for the overlap of p orbitals giving delocalisation which gives the 1,3 isomer extra stability and more energy is required to break the structure and so is less exothermic
Write an equation for the THEORETICAL hydrogenation of benzene, stating the expected enthalpy change
Write an equation for the ACTUAL hydrogenation of benzene, stating the expected enthalpy change
Explain why the theoretical value for the hydrogenation of benzene differs from the actual value
Kekule/theoretical structure assumes there is no delocalisation of p electrons/no delocalised ring which confers stability to the molecule
How much more stable is the actual structure of benzene compared to kekules structure
Benzene is 152KJmol-1 more stable (360 - 208)
Hydrogenation of benzene is 152KJmol-1 less exothermic than the theoretical molecule
What are the 2 electrophiles which can react with benzene in electrophilic substitution
Nitronium ion (NO2+)
Acylium ion (RCO+)
What is the name of the mechanism for the nitration of benzene
Electrophilic substitution
What is the name of the mechanism for the acylation of benzene
Electrophilic substitution
Name and outline the mechanism for the nitration of benzene
Electrophilic substitution
Name and outline the mechanism for the acylation of benzene
Electrophilic substitution
What are the 3 stages in either nitration or acylation of benzene
1- Generation of electrophile
2- Mechanism
3 - Regeneration of catalyst
What catalyst is used in the acylation of benzene?
AlCl3
Write an equation for the generation of the acylium ion
Write an equation for the regeneration of the catalyst used in the acylation of benzene
What is the overall equation for the acylation of benzene
C6H6 + RCOCl —> C6H5COR + HCl
What is the reagent, catalyst and conditions required for the acylation of benzene
Reagent: RCOCl
Catalyst: AlCl3
Conditions: Anhydrous conditions, reflux, 50 degrees C
What catalyst is used in the nitration of benzene?
H2SO4
Write an equation for the generation of the nitronium ion in the nitration of benzene
Write an equation for the regeneration of the catalyst used in the nitration of benzene
What is the overall equation for the nitration of benzene
C6H6 + HNO3 —> C6H5NO2 + H2O
What is the reagent, catalyst and conditions required for the nitration of benzene
Reagent: Concentrated HNO3
Catalyst: Concentrated H2SO4
Conditions: Room temperature and pressure
What is the name of the molecule produced from the nitration of benzene
Nitrobenzene
What is the general name of the molecule produced from the acylation of benzene
Phenylketone
What is the theoretical benzene molecule called
cyclohexa-1,3,5-triene
Why does benzene undergo substitution and not addition
Benzene is stable, therefore they do not undergo electrophilic addition reactions as it would disrupt the stable ring of electrons
Why is the acylation of benzene important
Benzene is widely used, yet due to its stability it is difficult to react, acylation can help to solve this by weakening the structure of benzene making it easier to modify into useful products
Why is the nitration of benzene useful
Allows us to
Make dyes for clothing by reducing nitrobenzenes to aromatic amines
Making explosives such as TNT
Why is an aqueous solution obtained in the reduction of nitrobenzene even though phenylamine is insoluble in water.
C6H5NH2 present as ionic salt
