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 n_p(O)- - -π(Nap) interaction, which results in CT from n_p(O) to π(Nap) since O in 1−4 is highly electron rich due to the polar Se⁺=O^- bond and π(Nap) acts as an acceptor. There are two types of n_p(O)'s, n_py(O) and n_pz(O), if the directions of the Se−O bond and the p-orbitals of π(Nap) are taken in the x- and z-axes, respectively. Double but independent n_p(O)- - -π(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 n_p(O)→π(Ar) type in 1, in addition to the n_p(O)- - -π(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 n_p(G)- - -σ*(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)- - -σ*(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.