Structures of 1-(Arylseleninyl)naphthalenes:  O, G, and Y Dependences in 8-G-1-[<i>p</i>-YC<sub>6</sub>H<sub>4</sub>Se(O)]C<sub>10</sub>H<sub>6</sub>

Structures of 8-G-1-[<i>p</i>-YC<sub>6</sub>H<sub>4</sub>Se(O)]C<sub>10</sub>H<sub>6</sub> [<b>1</b> (G = H), <b>2</b> (G = F),<b> 3</b> (G = Cl), and<b> 4</b> (G = Br):  Y = H, OMe, OCH<sub>2</sub>Ph, <i>t</i>-Bu, Me, Cl, and NO<sub>2</sub>] and (1-C<sub>10</sub>H<sub>7</sub>)<sub>2</sub>SeO (<b>5</b>) are investigated by the X-ray crystallographic analysis. Structures of <b>1</b> are all <b>A</b> with regard to the naphthyl group (<b>1</b> (<b>A</b>)), where the Se−C<sub>Ar</sub> and Se−O bonds are perpendicular to and parallel to the naphthyl plane, respectively. Those of <b>2−4</b> are also <b>A</b>. Since structures of 8-G-1-(<i>p</i>-YC<sub>6</sub>H<sub>4</sub>Se)C<sub>10</sub>H<sub>6</sub> [<b>7</b> (G = F),<b> 8</b> (G = Cl), and<b> 9</b> (G = Br)] are all <b>B</b>, the results exhibit that <b>B</b> of <b>7</b>−<b>9</b> change dramatically to <b>A</b> of <b>2</b>−<b>4</b> with the introduction of O atoms. The factor to determine the <b>A</b> structures of <b>1</b>−<b>4</b> by O is called O dependence. The origin of the O dependence is the nonbonded n<sub>p</sub>(O)- - -π(Nap) interaction, which results in CT from n<sub>p</sub>(O) to π(Nap) since O in <b>1−4</b> is highly electron rich due to the polar Se<sup>+</sup>=O<sup>-</sup> bond and π(Nap) acts as an acceptor. There are two types of n<sub>p</sub>(O)'s, n<sub>py</sub>(O) and n<sub>pz</sub>(O), if the directions of the Se−O bond and the p-orbitals of π(Nap) are taken in the <i>x</i>- and <i>z</i>-axes, respectively. Double but independent n<sub>p</sub>(O)- - -π(Nap) interactions in <b>5</b> lead to <b>5</b> (<b>AA</b>). The conformation of the <i>p</i>-YC<sub>6</sub>H<sub>4</sub>Se group in <b>1</b> 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<sub>p</sub>(O)→π(Ar) type in <b>1</b>, in addition to the n<sub>p</sub>(O)- - -π(Nap) interaction. The structure around the SeO group in <b>1</b> is close to that of <b>5</b> (<b>AA</b>), if the accepting ability of the <i>p</i>-YC<sub>6</sub>H<sub>4</sub>Se group is similar to that of the naphthyl group. <b>A</b> of <b>2</b>−<b>4</b> are further stabilized by the n<sub>p</sub>(G)- - -σ*(Se−O) 3c−4e interactions, which are called G dependence. QC calculations performed on the methyl analogues of <b>1</b>−<b>4</b> (<b>11</b>−<b>14</b>, 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 <b>14</b> if the steric repulsion between Br and Se is contained in the G dependence. The value is roughly predicted as 20 kJ mol<sup>-1</sup>. The structures of <b>1</b>−<b>5</b> are well explained by O, G, and Y dependences.