Second-Order Splittings in the ESR Spectra of Organic Radicals

More lines than can be explained by first-order theory have been observed in the ESR spectra of several alkyl radicals in solution. The additional structure is predicted if the usual treatment is extended to second order in the coupling constants. This extension has been made in such a way as to eliminate the necessity of explicitly considering the 2n nuclear-spin wave functions which occur with spin-½ nuclei. The spectrum of the ethyl radical is used to demonstrate the agreement of actual spectra with the treatment presented here. A table is included which facilitates calculation of the second-order structure in the spectra of radicals containing spin-½ nuclei.