ESR Spectra of Free Radicals in Solution

FiGxmE 13.3. Ute ESR spectrum and energy levels for the hydrogen atom. 

It is to be noted that Ag, the isotropic electron-spin-nuclear-spin hyperline coupling constant, can be qualitatively related to the amount of time the unpaired electron spins in an -orbital on the nucleus in question the larger Ag, the greater the probability of finding the electron at the nucleus. 

Organic free radicals in solution generally exhibit hyperfine coupling with several nuclei. When the nuclei are chemically equivalent, the number of lines is given by 

Number of Equivalent Atoms with I = jl (n) Relative Intensities of ESR Lines Number of Lines (n + T) 

When an organic radical possesses two or more sets of equivalent atoms, the total number of lines in the ESR spectrum is given by 

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ESR spectra of free radicals in solution often show hyperfine structure due to several nuclei, particularly H, with the same coupling constant. The ESR spectrum of the methyl radical in Fig. 3.1 shows a line pattern with three equivalent protons (/ = Vi). The analysis by the diagram under the spectrum shows the construction of a stick pattern with an intensity ratio 1 3 3 1. 

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