ESR Spectra of Gamma-Irradiated Cotton Cellulose I and II

Irradiation of purified fibrous cotton cellulose I and cotton cellulose II (mercerized) with γ-radiation from Co"" gave products containing relatively stable free radicals, easily shown in electron spin resonance (ESR) spectra. The ESR spectrum of irradi ated cellulose I consisted ,of three, lines, and the spectrum of irradiated cellulose II consisted of five lines. The principal lines of both spectra occurred at about the free electron value, and the symmetry of the spectra indicated equal interaction of hydrogen nuclear spins with the free radical. In the case of the three-line spectrum of irradiated cellulose I, this could occur on the formation of a free radical on the cleavage of the H atom from C5, cleavage of the OH group from C6, or cleavage of the H atom from the OH group of C6. The principal line of the spectra for each of these radicals would probably occur at ahout the same value, but the interaction of the equivalent hydrogens on C6 with either of the radicals would result in a different line width splitting. C5 is the most likely site of the free radical due to the delocalizing effect of the oxygen atom to which it is attached. In the case of the observed five-line spectrum of irradiated cellulose II this could occur on the formation of two free radicals which individually yield three lines. The principal lines of the spectra of these radicals would occur at about the same value and the less intense lines, due to equivalent hydrogen interactions of each spectrum, would occur at different line widths. One radical would likely form at C5 as described for cellulose I and the second radical at C6 on the same anhydroglucose unit or on another anhydroglucose unit in the same unit cell by either H atom or OH group cleavage. The formation of this second radical in cellulose II, compared with one radical in cellulose I. is further, evidence of differences in the internal forces in the unit cell on change of the lattice type from I to II, This could, be interpreted as a rearrangement in hydrogen bonding in the unit cell of cellulose II, compared with cellulose I, through the —CH ₂OH (C6) group of the anhydroglucose unit. This bond ing would have a delocalizing effect on C6, thereby increasing the chances of forming a second radical.