Parallel Conformation of 2-Cyanoethyl Group

In the process of the photoisomerization, the produced 1-ce group would be more easily restored if the group has smaller repulsion from the surrounding atoms. The ratio of the R and S configurations should depend on the shape of the reaction cavity. The reaction cavities for the 2-ce groups of the 3mpy and 4mpy before photo-irradiation are compared in Fig. 5.27a, b, respectively. The space at the 

The crystal was irradiated with a xenon lamp at room temperature and the intensity data were collected before the crystal was decomposed. The molecular structure is shown in Fig. 5.30b. The produced 1-ce group has only R configuration at one site. The ratio of the photo-produced 1-ce group and the original 2-ce group became 73 27. Further irradiation was impossible to keep the single crystal form. 

The reaction cavity before photo-irradiation is shown in Fig. 5.31. The cavity size is considerably large, 17.2 although the height of cavity is very low. It is clear that the produced 1-ce group with R configuration is well accommodated in the cavity. It seems impossible to include the 1-ce group with 5 configuration in the cavity. 

When the Co-C bond is cloven by photo-irradiation, the closer hydrogen atom bonded to the C atom, HlOB, should be extracted by the cobalt atom at the first stage and then the cobalt atom makes a bond with CIO giving H lOB to C9. Since the 2-ce group takes a parallel conformation, one of the hydrogen atoms bonded to the C atom comes close to the Co atom, the distances of Co -HIOA and Co—HIOB being 3.83 and 3.04 A, respectively. This may be a reason why the parallel conformation is effective to the photoisomerization. 

About 73 % of the 2-ce group of the complex with heia as an axial base ligand was changed to the 1-ce group with retention of the single crystal form. Moreover, the reaction rate was considerably fast. This brought about an idea that the isomerization mechanism would be made clear if the structures before and after the reaction were analyzed by neutron diffraction. 

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