Structures of 1-(arylseleninyl)naphthalenes: O, G, and Y dependences in 8-G-1-[p-YC6H4Se(O)]C10H6.

Structures of 8-G-1-[p-YC6H4Se(O)]C10H6 [1 (G = H), 2 (G = F), 3 (G = Cl), and 4 (G = Br): Y = H, OMe, OCH2Ph, t-Bu, Me, Cl, and NO2] and (1-C10H7)2SeO (5) are investigated by the X-ray crystallographic analysis. Structures of 1 are all A with regard to the naphthyl group (1 (A)), where the Se-C(Ar) and Se-O bonds are perpendicular to and parallel to the naphthyl plane, respectively. Those of 2-4 are also A. Since structures of 8-G-1-(p-YC6H4Se)C10H6 [7 (G = F), 8 (G = Cl), and 9 (G = Br)] are all B, the results exhibit that B of 7-9 change dramatically to A of 2-4 with the introduction of O atoms. The factor to determine the A structures of 1-4 by O is called O dependence. The origin of the O dependence is the nonbonded np(O)- - -pi(Nap) interaction, which results in CT from np(O) to pi(Nap) since O in 1-4 is highly electron rich due to the polar Se+=O- bond and pi(Nap) acts as an acceptor. There are two types of np(O)'s, npy(O) and npz(O), if the directions of the Se-O bond and the p-orbitals of pi(Nap) are taken in the x- and z-axes, respectively. Double but independent np(O)- - -pi(Nap) interactions in 5 lead to 5 (AA). The conformation of the p-YC6H4Se group in 1 changes depending on Y (Y dependence), although the effect is not strong. The Y dependence is explained on the basis of the magnitude of CT of the np(O)-->pi(Ar) type in 1, in addition to the np(O)- - -pi(Nap) interaction. The structure around the Se=O group in 1 is close to that of 5 (AA), if the accepting ability of the p-YC6H4Se group is similar to that of the naphthyl group. A of 2-4 are further stabilized by the np(G)- - -sigma(Se-O) 3c-4e interactions, which are called G dependence. QC calculations performed on the methyl analogues of 1-4 (11-14, respectively) reproduced the observed structures, supported the above discussion, and revealed the energy profiles. The energy-lowering effect of the O dependence would be close to the G dependence of the nonbonded n(Br)- - -sigma(Se-O) 3c-4e interaction in 14 if the steric repulsion between Br and Se is contained in the G dependence. The value is roughly predicted as 20 kJ mol(-1). The structures of 1-5 are well explained by O, G, and Y dependences.