ESR Study of l -Alanine-1-13C Irradiated at Low Temperatures

The ESR spectra of l-alanine-1-13C, x irradiated at low temperatures (T < 150°K), have been examined. The spectra have been interpreted in terms of a carboxyl radical similar to those postulated for other irradiated organic acids. From the values of the 13C hyperfine tensor it has been confirmed that the unpaired electron is essentially a 22pπ-type electron located primarily on the carboxyl carbon and that this spin density interacts with the α proton. From the magnitude of the isotropic 13C hyperfine splitting it is found that the RCO2− structure is bent about 8° from planarity. The stable room-temperature fragment in irradiated l-alanine-1-13C exhibits essentially isotropic 13C splittings of 12.8 G.