ESR, ENDOR, and double ENDOR at 300 °K of DL-serine x irradiated at 340 °K, a new radical species

Abstract

When DL‐serine single crystals are x rayed at 300 °K or below, two stable radicals are observed at room temperature. One of these, IV, is of greater intensity than the other, V, and was previously identified. By irradiating at a slightly elevated temperature, ∼340 °K, the concentration of V becomes more intense than IV. In this work we report on a detailed study of V using ESR, ENDOR, and double ENDOR, all at room temperature. We have determined that V is and have obtained five hyperfine tensors representing one α‐H, two β‐H’s, the rotating amino H’s, and a fourth H which is probably in a neighboring molecule. We have also observed the ENDOR transition of the nitrogen. The α‐H tensor is somewhat unusual in that the isotropic term (−41.3 MHz) is considerably less than for a 2ρπ electron and of the same sign, but the anisotropic term is approximately the same (+31.9, +3.5, −35.4 MHz). This is consistent with our model since the bonding to the α‐carbon is strained and would not be expected to be pure sp².