Conformations of highly hindered aryl ethers. XXI-fragementation paths involving intramolecular π-complexes and cyclizations in the mass spectra of 2,4-dinitrophenyl 2′-alkylphenyl ethers

The mass spectrometric study of 2,4‐dinitrophenyl 2′‐R‐phenyl ethers (R  H, Me, Et, i‐Pr, tert‐Bu) showed that (1) fragmentation proceeds differently from unsubstituted and 4‐nitro‐substituted diphenyl ethers; (2) important fragmentation routes involve interannular migrations and cyclizations; (3) these occur between two groups ortho to the ether linkage while the ethers are in unfavorable endo, endo twist conformations; (4) the observed interannular interactions can be ustified by the existence in these compounds of an intramolecular π‐complex which stabilizes the sterically unfavorable conformation and explains the observed fragmentations.