Benzene And Phenol Flashcards
Atomic formula of benzene
C6H6
Sigma and pi bonding in benzene
C-C in ring is sigma (head on overlap of P orbitals)
Pi binds from side on overlap of P orbitals above and bellow benzene ring
Effect of delocalised electrons on benzene structure
1 delocalised e- per carbon (in P orbital)
Forms negative electron cloud above and below the plane of the ring
High electron density
delocalised electrons in the ring move in the opposite direction
Forms ring current
Very stable molecule
3 reasons against Kekulé structure
C-C bond length
Addition reactions
Enthalpy of hydrogenation
Why C-C bond length does not support Kekulé structure of benzene
All bonds one uniform length
Between C-C and C=C
Measured by X ray diffraction
If benzene was triene it would contain 3xC=C and 3xC-C
Why benzene addition reactions do not support Kekulé structure
Does not readily undergo addition reactions (like an alkene)
Benzene does not decolourise bromine water
Due to delocalised e-, ring current, stable
Reasons against the Kekulé structure: enthalpy of hydrogenation
Less exothermic than expected with 3x C=C
Stable due to delocalised electron stability
Observations of combustion of benzene with air
Burns with smoky luminous flame
Due to high C:H
Equation for combustion of benzene with air
C6H6 + 7.5O2 -> 6CO2 + 3H2O
Incomplete combustion of benzene in air
Large volume of O2 required
Often incomplete combustion
Unburnt carbon, yellow flame, smokey
C6H6 +1.5O2 -> 6C + 3H2O
Bromination of benzene: creation of strong electrophile
Br2 + FeBr3 -> FeBr4- + Br+ (Strong electrophile)
Bromination of benzene overall reaction
Benzene + Br2 (FeBr3 reflux) -> 1-bromobenzene + HBr
Chlorination of benzene: overall reaction
Create electrophile same as bromination but using AlCl3
Benzene+ Cl2 (AlCl3 + reflux) -> 1-chlorobenzene + HCl
Nitration of benzene: formation of strong electrophile
HNO3 + H2SO4 -> NO2+ (electrophile) + HSO4- + H2O
Nitration of benzene: overall reaction
Benzene (HNO3 + H2SO4) -> benzene nitrate
