| Abstract
| - The structures of 8-G-1-(p-YC6H4Se)C10H6 (1 (G = Cl) and 2 (G = Br): Y = H (a), OMe (b), Me (c),Cl (d), Br (e), COOEt (f), and NO2 (g)) were investigated by X-ray crystallographic analysis, NMRspectroscopy, and ab initio MO calculations. The structures of all members in 1 and 2 are concludedto be type B, which is in striking contrast to the type A structure for 4d−g (4 (g(n)), where G = H).The Se−Ci bond of the p-YC6H4Se group in 8-G-1-(p-YC6H4Se)C10H6 is almost perpendicular to thenaphthyl plane in type A, and it is located on the plane in type B. The chlorine and brominesubstitution at the 8-position in 1 and 2 dramatically changes the type A structure of 4 (g(n)) totype B. The nonbonded G- - -Se−C 3c-4e type interaction must contribute to stabilize the type Bstructure. The type B structure in 1 and 2 should also be more stabilized than the same structurein 4 by the 3c-4e type interaction: The structure of 4b is type B in the crystals and type B wouldbe more stable for 4c and might be for 4a in solutions. Ab initio MO calculations are performed on8-G-1-(p-YC6H4Se)C10H6, 8-G-C10H6SeH-1, and models HG- - -SeH2, where G = Cl, Br, and F, toclarify the reason for the dramatic change in the structures. The type B structure is optimized tobe more stable than the type A for all species examined, which supports the observations. Theenergy differences between type B and type A are larger for the models than for the naphthalenes.While the superiority of the type B for the former is Br > Cl ≫ F, that of the latter is Br ≈ Cl ≥F. These results show that the main factor of the structural change from type A to type B is thenonbonded G- - -Se−C 3c-4e interaction. The electronic effect of halogens through the naphthaleneπ-framework would also contribute to some extent, although the direct comparison of the evaluatedvalues between the naphthalene systems and the models is not so easy. Factors to stabilize thetwo structures of 1, 2, 4, and 8-(MeSe)-1-(p-YC6H4Se)C10H6 are reexamined from a viewpoint ofthe nonbonded G- - -Se−C 3c-4e interaction (G dependence), together with the electronic effect ofY (Y dependence).
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