The carbon has the positive charge for the electrophile
The product of acylating benzene is a phenylketone.
Benzene is cyclic, planar120 bond angle, molecule with the formula c6h6 (structure)
Carbon has 4 outer electrons, each carbon is bonded to 2 other carbons and 1 hydrogen atom. The final lone electron is in the p-orbital which sticks out above and below the planar ring (2 regions of high electron density)
Bonding: (3 bonds, 1 delocalised electrons per C)
P-orbitals overlap to form a delocalised ring of electrons (pi orbital)
Due to delocalised electron structure all the C-C bonds are the same (same bond length and strength)
Why the Kekule model was wrong
C-C bonds are not the same length
Kekule should be able to undergo electrophilic addition
the enthalpy change of hydrogenation expected to be 360kj mol -1 ( if the Kekule structure was correct, benzene should have 3x the enthalpy of hydrogenation as cyclohexene since it has 3x double bonds. Its actual enthalpy of hydrogenation is much less exothermic, suggesting that the structure is more stable than the structure proposed by Kekule.)
(difference) 152 (more stable)
less energy released
more energy to break reactant bonds
Benzene is stable due to the delocalised ring of electrons so is unreactive
The increase in stability connected to delocalisation is called the delocalisation energy
Explain the structure and bonding of benzene
every C has 3 bonds, spare electrons in p orbitals overlap ( to form a pi cloud), c
planar, 120 degree bond angle, 6 carbon ring, C-C bond equal in length
expected delta Hhydrogenation of cyclohexatriene = -360
delta hydrogenation difference in 152
benzene is lower in energy than cylcohexatriene/ more stable