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

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Abstract
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 hyperfinetensor 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.