Chapter 25 Benzene Flashcards
What can the ring in benzene be called?
π system or delocalised electrons ring.
How many P orbitals overlap together; and how many electrons are delocalised?
6 P orbitals; and 6 electrons are delocalised.
Describe the shape of benzene
1) All 6 carbons are sp₂ hybridised and the geometry of the carbons are trigonal planar at 120°.
2) Atoms are in the same plane in a hexagonal shape.
3) C-C bonds have sigma bonds where sp₂ hybridised orbitals have overlapped; and also pi bonds where the P orbitals have overlapped to form the π system which contains 3 pairs of delocalised electrons.
4) C-H bonds have only sigma bonds where sp₂ hybridised orbital of C and S orbital of H, overlap.
Which type of reaction does Benzene generally undergo?
Electrophilic substitution.
When benzene reacts, the π system…
…remains intact.
Which type of reaction do Acyl chlorides generally undergo?
Nucleophilic condensation.
If a species X is bonded to a benzene molecule, state when carbon 2,4,6 is activated and when carbon 3,5 is activated:
1) If X has lone pairs or positive inductive effect, it will donate the electron cloud and the lone pairs will partially overlap with the π system and activate carbon 2,4,6.
2) If X has no lone pairs or no positive inductive effect, it will withdraw the electron cloud and activate carbon 3,5.
Alcohol reactions with Na, NaOH, Na₂CO₃:
Alcohol + Na—>YES
Alcohol + NaOH—>NO
Alcohol + Na₂CO₃—>NO
Phenol reactions with Na, NaOH, Na₂CO₃:
Phenol + Na—>YES
Phenol + NaOH—>YES
Phenol + Na₂CO₃—>NO
Carboxylic acid reactions with Na, NaOH, Na₂CO₃:
Carboxylic acid + Na—>YES
Carboxylic acid + NaOH—>YES
Carboxylic acid + Na₂CO₃—>YES
ACIDITY COMPARISION WEAKEST TO STRONGEST ACIDITY phenol,carboxylic acid, alcohol:
Alcohol<Phenol<Carboxylic acid.
Why is benzene more stable and less reactive than alkyl benzenes or alkenes?
The delocalised electrons are spread all over the benzene molecule.
