4.
Which of the following can chelate metals, among salicylaldehyde, salicylic acid, and o-
nitrophenol?
a. salicylaldehyde
b. salicylic acid
c. o-nitrophenol
d. all of these
All three compounds—salicylaldehyde, salicylic acid, and o-nitrophenol—can chelate metals due to their donor atoms with lone pairs. The correct answer is d. all of these.
Option Analysis
Salicylaldehyde features a phenolic OH and ortho aldehyde group (O from C=O), forming bidentate chelates with metals like Fe³⁺ and Cu²⁺ via O,O-coordination. Its derivatives serve as ligands in Schiff bases for stable metal complexes.
Salicylic acid has ortho phenolic OH and carboxylate (COO⁻), enabling strong bidentate O,O-chelation with transition metals such as Mn²⁺, Fe³⁺, and Cu²⁺. This structure supports chelate resins for heavy metal adsorption.
o-Nitrophenol possesses phenolic OH and ortho nitro (NO₂) group, where oxygen lone pairs allow monodentate or chelate formation in mixed ligand complexes with Co²⁺ and Ni²⁺. Intramolecular H-bonding influences but does not prevent metal binding.
Chelation Mechanism
Chelation requires adjacent donor atoms for ring formation. Salicylaldehyde and salicylic acid excel in five-membered rings via ortho OH and carbonyl/carboxyl groups. o-Nitrophenol uses OH and nitro oxygen, often in mixed systems. All exhibit heteroatoms (O, N) for metal coordination.
