Electron paramagnetic resonance derivative spectrum

Fig. 2. Electronic paramagnetic resonance spectrum, recorded at v = 9 32 GHz and ff = 3290 Oe as its first derivative, of the radical appearing after irradiation with U-V light of A = 2S4 nm at 77°K of a frozen 5 X 10 M aqueous solution of thymine containing K4Fe(CN)g as a source of electrons. The coupling of the odd electron with the protons on Cg should theoretically yield a triplet (A), but each component of this triplet is further split into four lines (B) as a result of coupling with the three protons of the methyl group. The theoretical spectrum reconstruct in the lower part of the figure shows how the summation of these 12(3X4) components accounts for the distribution and intensity of the eight observed lines.

Polymers or frozen solvents have several disadvantages as trapping media for the spectroscopic study of reactive species. First, they are often not chemically inert to very reactive species, such as metal atoms and carbenes. Second, they absorb strongly over large regions of the IR spectrum. Since much more structural information about trapped molecules can usually be derived from IR than from UV-visible or electron paramagnetic resonance (EPR) spectroscopy, the latter is a severe problem. 

Solutions of sodium-naphthalene in tetrahydrofuran are dark green, electrically conducting because the compound is a salt Na (THF) CioHs", and paramagnetic because of the extra electron which is in a singly occupied 7r-orbital. Information about the distribution of the unpaired electron about its various possible positions in the anion can in suitable cases be derived from the electron spin resonance spectrum. If the orbital occupied by the unpaired electron in a hydrocarbon anion is non-degenerate, as is the case with naphthalene and anthracene, then a second electron (formation of anion ) would enter the same orbital and both the paramagnetism and e.s.r. spectra disappear. 

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