ESR study of calix[4]arene by spin-trapping method

Electron spin resonance (ESR) measurements are introduced to investigate the interaction between 5,11,17,23-tetrabromo-25,26,27,28-tetramethoxycalix4]arene (II ₄) and 2-methyl-2-nitrosopropane (MNP) or nitrosodurene (ND) which are used as spin-trapping reagents under ultraviolet irradiation. In most cases, the complicated ESR spectra were observed because of the overlap of ESR signals attributed to several spin adducts in different conformations or in an inclusion state. However, after the optimum amount of ND was added into theII ₄ solution, the ESR spectrum showed that each nitrogen hyperfine line was further split to 1:2:1 triplet lines, and this is a typical spectrum ascribed to the spin adduct of ND at one para position ofII ₄.