| Abstract
| - 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-raycrystallographic analysis. Structures of 1 are all A with regard to the naphthyl group (1 (A)), where theSe−CAr and Se−O bonds are perpendicular to and parallel to the naphthyl plane, respectively. Those of2−4 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 Oatoms. The factor to determine the A structures of 1−4 by O is called O dependence. The origin of theO dependence is the nonbonded np(O)- - -π(Nap) interaction, which results in CT from np(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 np(O)'s, npy(O) and npz(O), if the directions of the Se−O bond and the p-orbitalsof π(Nap) are taken in the x- and z-axes, respectively. Double but independent np(O)- - -π(Nap) interactionsin 5 lead to 5 (AA). The conformation of the p-YC6H4Se group in 1 changes depending on Y (Ydependence), although the effect is not strong. The Y dependence is explained on the basis of the magnitudeof CT of the np(O)→π(Ar) type in 1, in addition to the np(O)- - -π(Nap) interaction. The structure aroundthe SeO group in 1 is close to that of 5 (AA), if the accepting ability of the p-YC6H4Se group is similarto that of the naphthyl group. A of 2−4 are further stabilized by the np(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 energyprofiles. The energy-lowering effect of the O dependence would be close to the G dependence of thenonbonded n(Br)- - -σ*(Se−O) 3c−4e interaction in 14 if the steric repulsion between Br and Se iscontained in the G dependence. The value is roughly predicted as 20 kJ mol-1. The structures of 1−5 arewell explained by O, G, and Y dependences.
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