Single crystal neutron diffraction study of a crystalline-state photoisomerization by using a new TOF-Laue neutron diffractometer SENJU at J-PARC

Ohara, Takashi   ; Kiyanagi, Ryoji  ; Oikawa, Kenichi   ; Kawasaki, Takuro   ; Kaneko, Koji   ; Tamura, Itaru  ; Nakao, Akiko*; Hanashima, Takayasu*; Munakata, Koji*

Single crystal neutron structure analysis is a powerful tool to study crystalline-state reactions because of its ability to distinguish deuterium atoms from hydrogen atoms. When the hydrogen atoms in specific positions of the reactive group are exchanged with deuterium atoms and the crystalline-state reaction proceeds, the hydrogen/deuterium migration in the reaction is easily observed by the neutron diffraction analysis and consequently the reaction mechanism is estimated. In this study, we performed a single crystal neutron diffraction measurement of a 3-cyanopropyl cobaloxime complex by using the same crystal of the previous study and a new TOF-Laue type single crystal neutron diffractometer SENJU at J-PARC. The result of the structure refinement showed that the chiral H-C*-D methylene group in the photo-produced 1-cyanopropyl group has the racemic form and an energy calculation suggested that one configuration was more preferable than the other. This indicates that the olefin formation and the racemization of the H-C*-D methylene group occurred after the 1-cyanopropyl group was formed by continuous photo-irradiation as predicted in the previous research.