Aromatic chemistry Flashcards
What is the structure in benzene?
- A planar cyclic structure
- 120 bond angle
properties of -Arenes
- high melting points due to the stability of the ring of electrons
- low boiling points as they are non-polar
- cannot be dissolved in water
properties of benzene
- colourless or light yellow liquid at room temprature
- sweet odor
- highly flammable and produces a sooty flame
What type of reaction does benzene not undergo?
Electrophilic addition
What is the enthalpy of hydrogenation of benzene?
208 kJ/mol
What is the enthalpy of hydrogenation of 1,3,5-cyclohexatriene?
360 kJ/mol
What is the enthalpy of hydrogenation of cyclohexene?
120 kJ/mol
What does benzene having a lower enthalpy of hydrogenation than a theoretical 1,3,5-cyclohexatriene mean?
That it is more stable (the number being lower shows the reaction is less exothermic, so more energy must have been put in to break bonds)
Why is benzene more stable than expected?
Due to the delocalised electrons, electron density is shared over more atoms, which means the energy of the molecule is lowered and it is more stable
Where do the delocalised electrons in benzene come from?
The final unpaired electron in each carbon is located in a p orbital which sticks above and below the carbon, and together with the other orbitals forms a ring of delocalised electrons
What is the length of a bond in benzene compared to a single C-C and double C=C bond?
It is somewhere in the middle
When you see ‘phenol’ in a compound name, what does this mean?
This denotes a benzene ring as a subsidiary group, similar to a methyl group
What are the 2 types of electrophilic substitution which benzene goes through?
- Nitration
- Friedel-Crafts Acylation
What are the conditions for nitration of benzene?
50 degrees celcius, concentrated HNO3 and H2SO4
Why does benzene nitration need a supercharged electrophile?
It is too stable to be attacked by normal electrophiles
