Structure of 1-(Arylselanyl)naphthalenes − Y Dependence in 1-(p-YC6H4Se)C10H7

The structures of 1-(arylselanyl)naphthalenes [1-(p-YC6H4Se)C10H7 (1), where Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOEt (f), and NO2 (g)] were determined. The structures of 1 were well classified using types A, B, and C, where the Se−CAr bond in 1 is placed almost perpendicular to the naphthyl plane in type A and is located on the plane in type B. The type C structure is intermediate between type A and type B. The structures of 1d−1f are demonstrated to be type A whereas that of 1b is type B by X-ray crystallographic analysis. The type B conformer is suggested to be favorable in solutions for 1a and 1c based on the NMR-spectroscopic data. The structure of 1g is assumed to be type A. These results show that the stable structure of 1 must be type A or type B, contrary to early observations of type C for 1,8-bis(alkyl- or arylchalcogeno)naphthalenes. Consequently, the structure of 1 changes dramatically depending on Y in the solid state. We propose that these structures can be explained by the electron affinities, together with the energies of LUMO and LUMO+1 of benzene, substituted benzenes, and naphthalene, which are the components of 1. In order to clarify the reason for the dramatic change in the structure of 1 with change in Y, ab initio MO calculations were performed on 1 and related compounds. The type A and type B conformations were optimized as stable molecules. Although 1a (type A) is predicted to be more stable than 1a (type B) by 1.3 kJ mol−1, the latter becomes more stable than the former by 8.4 kJ mol−1 if the solvent effects of chloroform are taken into account in the calculations, which was done by applying the IPCM method. The transition state between type A and type B in 1a is similar to type C, which must prevent the monotonical change in the structure of 1. Compound 1 would be in equilibrium between type A and type B in solutions. The results of the MO calculations on 1 suggest that type A is exclusive for 1g, and probably exclusive for 1f, and predominant for 1d and 1e, while type B is predominant for 1b. The type A and type B would be comparable for 1a and 1c.