27 - Aromatic chemistry Flashcards
How are pi electrons organised in benzene?
Delocalised
What is benzene’s chemical formula?
C6H6
How long is a Benzene C-C bond? and how strong?
Between single and double C bond
What is benzene more thermodynamically stable than?
cyclohexa-1,3,5-triene
What is the increase in stability connected to delocalisation called?
Delocalisation energy
Why does benzene not undergo addition reactions?
This would break up the delocalised system
Why does benzene undergo electrophilic substitution?
High electron density
What is the electrophile in nitration?
NO2+
What condition(s) are needed for nitration?
Conc sulfuric acid
55C
What is nitration used to synthesise?
- Explosives
- Amines
What is the reaction to generate a nitronium electrophile?
Conc HNO3 + 2Conc H2SO4 goes to NO2+ + 2HSO4- + H3O+
What is the functional group change in Friedel Crafts acylation?
Benzene changes to phenyl ketone
What are the conditions for a Friedel Craft acylation?
Heat under reflux (50C)
Anhydrous aluminium chloride catalyst
What is the mechanism for a Friedel Craft acylation?
Electrophilic substitution
What is the electrophile for a Friedel Craft’s acylation?
RCO+
What is the equation for the formation of the electrophile in a Friedel Craft acylation?
AlCl3 + CH3COCl goes to [Ch3CO]+ + [AlCl4]-
How can a nitroarene be reduced to an aromatic amine?
[H]
Heat, Sn and HCl
Forms water
Hydrogenation with H2 and Ni catalyst
Explain the bonding in and the shape of a benzene molecule. Compare the stability of benzene with that of the hypothetical
cyclohexa-1,3,5-triene molecule, using thermochemical data given. (6)
- Each Carbon has 3 covalent bonds
- Spare electrons overlap
- Delocalisation
- Planar
- 6 Carbon ring
- C-C bond lengths between single and double bond
- Expected hydrogenation of cyclohxatriene = -360
- hydrogenation of benzene less exothermic by 152
- Benzene more stable
Why is minimum quantity of hot water used? (1)
Ensure hot solution is saturated with product
Why is flask cooled to room temperature before crystals were fiiltered off?
Yield is lower if warm
Why are crystals compressed in the funnel?
Air passes through sample not around it
Why is a little cold water passed through crystals?
Remove insoluble impurities
