Structure of 1-(arylselanyl)naphthalenes - Y dependence in 1-(p-YC6H4Se)C10H7

The structures of 1-(arylselanyl)naphthalenes [1-(p-YC6H4Se)C10H7 (1), wher e 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-C-Ar bond in 1 is placed almost perpendicular to the naphth yl plane in type A and is located on the plane in type B. The type C struct ure 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 crystallogr aphic analysis, The type B conformer is suggested to be favorable in soluti ons 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 t hese structures Can be explained by the electron affinities, together with the energies of LUMO and LUMO+1 of benzene, substituted benzenes, and napht halene, which are the components of 1. In order to clarify the reason for t he dramatic change in the structure of 1 with change in Y, ab initio MO cal culations were performed on 1 and related compounds. The type A and type B conformations were optimized as Stable molecules. Although 1a (type A) is p redicted to be more stable than 1a (type B) by 1.3 kJ mol(-1), the latter b ecomes 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 b y 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 th e structure of 1. Compound 1 would be in equilibrium between type A and typ e B in solutions. The results of the MO calculations on 1 suggest that type A is exclusive for 1g, and probably exclusive for If, 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.