6.1.1 - Aromatic Compounds Flashcards
Blurt everything you know about benzene’s structure
Further summary for Sigma bonds In terms of benzene ring
- Direct overlap of orbitals between bonding atoms (head-on overlap).
- Electron density is concentrated between the atoms, so it’s easier to find electrons in the bond.
- Stronger than pi bonds due to the direct overlap.
- Free rotation around the bond axis because the bond doesn’t disrupt the molecule.
- Formed by overlap of s - and p -orbitals (or p -orbitals in single bonds).
- 3 sigma bonds for each carbon atom in a benzene
Further summary for pi bonds In terms of benzene ring
1.Sideways overlap of p-orbitals above and below the bonding atoms.
2.Electron density is spread out above and below the bond, so there’s a lower probability of finding the electron in any specific area.
- Weaker than sigma bonds due to the less effective overlap.
- Restricts rotation because it would disrupt the delocalized electron cloud.
- Present only in double or triple bonds (with sigma bonds).
Compare the delocalized model and Kekulé structure of benzene in terms of π bonding and electrons.
- Delocalised model
- Each carbon atom has one p-orbital, In each orbital there is one electron spread out. So when all the p orbitals from each carbon atom overlap sideways to form 1 pi bond there will be six electrons in the pi bond.
- Electrons are delocalised
- Kekule’s structure
- For the 3 double bonds it consists of one sigma bond and one pi bond.
- A pi bond is formed when two p orbitals overall.
- Therefore in total since there are 3 double bonds there is also only 3 pi bonds.
- In each pi bond there will be 2 electron as there are 2 p orbitals (which consist of one electron each) that overlap to form one pi bond.
- Electrons are localised.
If we were to look at the enthalpy change of hydrogenation for the delocalised model and for kekules structure would it be the same for both models or different ?
The enthalpy change of hydrgenation for the delocalised model is less exothermic than expected when compared to the enthalpy change of hydrogenation for kekules structure
- This is because of the delocalise ring system which makes the model more stable
Which type of reactions do benzenes undergo and explain why they wouldn’t undergo other reactions.
- Electrophilic substitution reactions
When bromine is near an alkene it undergoes an addition reaction, why doesn’t arene‘s undergo theses same addition reactions
- The delocalised ring system decreases its electron density so bromine isn’t polarised near an arene’s and therefore wouldn’t undergo an addition reaction.
-Benzene is also stable so unlike traditional alkenes they do not undergo electrophilic addition reactions (like the bromination of alkene) as this would disrupt the stable ring of electrons.
What is benzene used in ?
Dyes and pharmaceuticals
What do you know about the toxicity of benzene ?
Blurt everything you know about friedel-crafts acylation
Including the change in functional group, the formation of the electrophile, the mechanism, the reformation of the catalyst etc.
- Use the example of ethyl chloride
Blurt everything you know about friedel-crafts alkylation
Including the change in functional group, the formation of the electrophile, the mechanism, the reformation of the catalyst etc.
- Use the example of chloroethane
Blurt everything you know about the nitration of benzene’s Including the change in functional group, the formation of the electrophile, the mechanism, the reformation of the catalyst etc.
What happens if you carry out nitration at temperatures above 50 degrees
2 nitrate groups will be substituted
Blurt and draw everything you know about bromination
Blurt and draw everything you know about chlorination
Why are phenols much more reactive than benzene’s
(In phenol) a (lone) pair of electrons on O is(partially)
delocalised
Electron density is therefore higher (than benzene)
(phenol) is more susceptible to electrophilic attack
- Phenols are electron donating groups.
What are electron withdrawing groups and give an example of them
What are electron donating groups and give an example of them
Phenol can partiallly dissociate, what does this mean for them ?
- This means that they are weak acids and will therefore react like acids do .
Phenols can react more readily with bromine than benzene’s please blurt, draw and outline everything you know about the reaction of benzene and bromine icon. The uses, the products etc.
Blurt, outline and draw everything you can remember about the reaction of phenol with nitric acid
- OH group are 2,4 directing so will place the nitrate groups in this position
What do you understand about the effect of delocalisation on a chlorine, -OH and amine side groups
Why is benze delocalised more stable
