1) HCOOH + PCl5 ⇒ HCOCl + POCl3 + HCl 1) nu e reacie redox
2) HCN + CH3-CO - CH3 = CH3-(HO)C(CH3) -CN
in CH3-CO -CH3 , -C⁺²O - , in produsul de reactie -(HO)C⁺¹(CH3) -CN
2) = reactie redox
3) nu
4) C⁻²H2=C(CH3)-CH3 + Cl-C⁻¹H2- (Cl)C(CH3) - CH3 este redox