6.1 Aromatic Compounds, Carbonyls And Acids Flashcards
Describe Kekule’s model of benzene
Six-membered ring with alternating single and duble bonds between the carbon atoms
What are the 3 features of benzene that don’t support Kekule’s model?
- Benzene is resistant to addition reactions unlike alkenes
- Enthalpy chane of hydrogentaion of benzene is more stable than predicted
- All the carbon bonds have the same length instead of 3 short C=C bonds and 3 long C-C bonds
What technique was used to find the bond lengths of benzene?
X-ray diffraction
What happens to the 4th electron in the p-orbital of each carbon atom in benzene?
It delocalizes to form rings of electron density above and below the molecule
How do the rings of electron density affect the stability of benzene?
Makes benzene very stable, even though it is unsaturated (aromatic stability)
Is benzene soluble in water? Why?
No because it’s non polar
How do you name compounds containing a benzene ring?
-benzene, or phenyl- ;can designate position on ring using numbers if there is more than one substituent
Why is benzene attacked by electrophiles?
High electron density above/below ring due to delocalised electrons
- Whats’ an electrophilic substitution ?
2. What’s a reaction mechanism?
- a substitution reaction where an electrophile is attracted to an electron-rich atom/ part of a molecule and a new covalent bond is formed by the electrophile accepting an electron pair
- a model with steps to explain and predict a chemical reaction
Nitration of benzene is what type of reaction ?
Electrophilic substitution reaction
Which ion is used to nitrate benzene?
NO2+
What is the catalyst in nitration of benzene?
Concentrated sulfuric acid
How is NO2+ ion generated?(conditions and equations)
Conc. H2S04, Conc, HNO3
H2S04 + HNO3 -> HSO4- + NO2+ + H20
How is the H2SO4 catalyst regenerated in the nitration of benzene?
HSO4- + H+ ->H2SO4
What type of catalyst is used for a Friedel-Crafts reaction?
A halogen carrier (AlCl3, FeBr3)
Why does benzene not react directly with halogens?
There isn’t enough electron density between the carbon atoms to induce a dipole in a non-polar halogen
How is the ALCL3 catalyst reformed?
AlCl4- + H+ -> AlCl3 +HCl
How could you use a Friedel-Crafts mechanism to add a methyl group to benzene ring?
Use a halogenalkane and AlCl3 to create a electrophile that can attack benzene
What reactions can you carry out to show the weak acidity of phenol?
A neutralisation reaction with NaOH occurs but absent when you react phenol with carbonates
Why can phenol undergo electrophilic substitution with relative ease?
Because phenol is more reactive than benzene due to p-orbitals electrons from the oxygen add to the delocalised electron ring which increases electron density so it’s more nucleophilic
What is the directing effect of electron donating groups OH and NH2?
Direct group to 2 and 4 position of the ring in electrophilic substitution of aromatic compounds (Donating groups)
What is the directing effect of electron withdrawing group NO2 ?
Direct group to the 3 position of the ring in electrophilic substitution of aromatic compounds (Withdrawing group)
What is the carbonyl group?
C=O
