6.1 Flashcards
Problems with kekule’s model
- Benzene is resistant to addition reactions
- Enthalpy of HYDROGENATION is higher (-208 compared to -360 kJmol-1) which shows benzene is more stable
- All 6 C-C bonds are the same length
Hydrogenation
addition of hydrogen to an unsaturated chemical
When is a aromatic compound called phenyl-?
When 1 hydrogen has been removed from the ring
What are the conditions for nitration of benzene?
-concentrated nitric acid (HNO3)
-H2SO4 catalyst
-Reflux
HNO3 + H2SO4 —-> NO2+ + HSO4- + H2O
What is the equation for the halogen carrier for halogenation of benzene?
Br2 + FeBr3 —> Br+ FeBr4-
Friedel-Crafts acylation
Acyl chloride used
Forms a ketone
Is an electron withdrawing group so only substitutes once
What does phenol react with and why?
Reacts with strong bases = O-Na+
Doesn’t react with carbonates
This is because it is a weak acid - it partially dissociates in H2O
Bromination of phenol
Triple substitution of Br in 2,4,6
Nitration of phenol
If dilute, single substitution of NO2 on 2 or 4
If concentrated, triple substitution of NO2 in 2,4,6
Doesn’t require a catalyst like benzene
What determines the position of substitution?
The group that is already on the benzene ring
Electron donating groups
OH, NH2
2,4 directing
Electron withdrawing groups
NO2
3 directing
Reactions with carbonyls
Oxidation
Nucleophilic addition:
-reduction = NaBH4 + H2O
-hydrogen cyanide (HCN)
Trends in solubility of carboxylic acids
Smaller the carboxylic acid, the more soluble it is
Because it is the end that forms the hydrogen bonds
Reactions of carboxylic acids
Reacts with metals to form salts
eg. HCOO-Na+ sodium ethanoate
