Aromatic Hydrocarbons and Carcinogenicity

Aromatic compounds :
They should obey the following Huckel's rule. i.e., (4n + 2)π electron. Here n = 0, 1, 2, 3 -------. It is also called (4n + 2) rule.
ex : Benzene C₆H₆ - 6π electrons.
Anti aromatic compounds :
1. Molecule is cyclic, planar it should contain 4π e⁻
In the ring at each atom 'P' - orbital should be present.
ex : Cyclo butadiene

Non - aromatic compounds :
All atoms should not contain P - orbitals in the ring.
Stability order
Aromatic > Non aromatic > Anti aromatic
Stability between aromatic and anti aromatic

Nitration :

For nitration reactivity order
C₆H₆ = C₆D₆ = C₆T₆
N₂O₅ solid \left(NO_2^+ , NO_3^{-}\right)
Fuming nitric acid (fumes of NO₂ with conc HNO₃)
NO_2^+ , ClO_4^{-}
AC_{2}O + N_{2}O_{5}
      ↓
(CH_{3}CO)_{2}

Sulphonation :

Rate of sulphonation :
C₆H₆ > C₆D₆ > C₆T₆

Ortho para directing (or) Activating groups :
           
OH, NH₂, NH₃, NHCOCH₃, OCH₃, CH₃, C₂H₅ ----- etc
Meta directing groups / Deactivating groups :
NO₂, CN, CHO, COR, COOH, COOR, SO₃H ----- etc.
Note : (Halogens)Cl ⇒ Deactivating group ⇒ inductive effect ⇒ O and P directing group ⇒ resonance.