INFRARED SPECTRAL STUDY OF CROWN-ETHER MOLECULAR-COMPLEXES WITH 4-NITROANILINE

The IR spectra of the crystalline complexes of 4-nitroaniline with cro wn ethers were studied, viz., 18-crown-6, benzo-18-crown-6, dibenzo-18 -crown-6, dicyclohexano-18-crown-6 and dibenzo-24-crown-8. The hydroge n bonding interaction was found to be predominant in these complexes. The strongest among them was the one formed with the most flexible cro wn ether dicyclohexano-18-crown-6, in which both the N-H bonds of 4-ni troaniline were shown to be equivalently hydrogen bonded to the crown ether oxygens. The shift of the NO2 absorption bands indicated that th e resonance form (-O2N-C6H4=N+H2) is favored upon complexation with th e larger ring size dibenzo-24-crown-8, while for the other complexes, the resonance form (O2N-C6H4-NH2) is favored; a fact which was attribu ted to geometrical factors.