Fine Structures of 8-G-1-(p-YC6H4C ≡ CSe)C10H6 (G = H, Cl, and Br) in Crystals and Solutions: Ethynyl Influence and Y- and G-Dependences

Fine structures of 8-G-1-(p-YC6H4C ≡ CSe)C10H6 [1 (G = H) and 2 (G = Cl): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f), and NO2 (g)] are determined by the X-ray analysis. Structures of 1, 2, and 3 (G = Br) are called A if each Se–Csp bond is perpendicular to the naphthyl plane, whereas they are B when the bond is placed on the plane. Structures are observed as A for 1a–c bearing Y of nonacceptors, whereas they are B for 1e–g with Y of strong acceptors. The change in the structures of 1e–g versus those of 1a–c is called Y-dependence in 1. The Y-dependence is very specific in 1 relative to 1-(p-YC6H4Se)C10H7 (4) due to the ethynyl group: the Y-dependence in 1 is almost inverse to the case of 4 due to the ethynyl group. We call the specific effect “Ethynyl Influence.” Structures of 2 are observed as B: the A-type structure of 1b changes dramatically to B of 2b by G = Cl at the 8-position, which is called G-dependence. The structures of 2 and 3 are examined in solutions based on the NMR parameters.

Structures of the naphthalene system are well explained by the three types, A, B, and C, in our definition, where the Se-C sp bond is perpendicular to the naphthyl plane in A, it is placed on the plane in B, and C is intermediate between employed for the structures around the Se-C Nap bonds in 1-6. The planar (pl) and perpendicular (pd) notations are also used to specify the structures of 1-6, where they specify the conformers around the Se-C ≡ C-C Ar (abbreviated Se-C Ar ) bonds in 1-3 and those around Se-C Ar in 4-6. Scheme 3 illustrates plausible structures of 1-3. Combined notations such as (A: pl) and (B: pd) are employed for the structures. The structures of 4 are B for Y of donating groups such as OMe, whereas they are A for Y of accepting groups such as NO 2 [22]. We call the results Y-dependence. The magnitude of the p(Se)-π(Ar/Nap) conjugation must be the origin of Y-dependence in 4.
Here, we report the fine structures of 1 and 2 determined by the X-ray crystallographic analysis as a factor to control the fine structures. We call the factor "Ethynyl Influence" in 1 and the G-dependence arise from the nonbonded n p (G)· · · σ * (Se-C sp ) 3c-4e interaction or the G· · · Se-C sp -C sp -C sp 2 5c-6e type interaction in 2 and 3. The behaviors of 1-3 in solutions are also examined, containing the selective 1 H, 13 C-NOE difference spectroscopic measurements, to estimate the efficiency of the factors based on NMR parameters.

Materials and Measurements.
Manipulations were performed under an argon atmosphere with standard vacuumline techniques. Glassware was dried at 130 • C overnight. Solvents and reagents were purified by standard procedures as necessary.
Melting points were measured with a Yanaco-MP apparatus of uncollected. Flash column chromatography was performed on silica gel (Fujisilysia PSQ-100B), acidic and basic alumina (E. Merck). 1-3 were prepared by the methods described elsewhere [67,68]. NMR spectra were recorded at 297 K on a JEOL AL-300 MHz spectrometer ( 1 H, 300 MHz; 77 Se, 57 MHz) on a JEOL ECP-400 MHz spectrometer ( 1 H, 400 MHz; 13 C, 100 MHz) in chloroform-d solutions (0.050 M) 2 . Chemical shifts are given in ppm relative to one of TMS for 1 H NMR spectra and relative to reference compound Me 2 Se for 77 Se NMR spectra.

Results and Discussion
3.1. Structures of 1 and 2 in Crystals. Single crystals were obtained for 1a-c, 1e-g, 2b, 2e, and 2g via slow evaporation of dichloromethane-hexane or ethyl acetate solutions. The Xray crystallographic analyses were carried out for a suitable crystal of each compound. One type of structure corresponds to 1b, 1c, 1e-g, 2b, 2e, and 2g and two-type ones to 1a in the crystals. The crystallographic data and the structures are reported elsewhere [66,67]. Figure 1 summarizes structures of 1 and 2, relative to 4-6. Table 1 collects the selected interatomic distances, angles, and torsional angles, necessary for the discussion. The atomic numbering scheme is shown for 1b in Figure 1, as an example.
As shown in Figure 1 and Table 1, the structure of 1 is A for Y of nonacceptors (1 (A)) such as H (a), OMe (b), and Me (c), whereas that of 1 is B for Y of acceptors (1 (B)) such as Cl (e), CN (f), and NO 2 (g) (Scheme 2). The results are quite a contrast to the case of 4, where the structure of 4 is B with Y = OMe, and they are A when Y = Cl and NO 2 . The ethynyl group interrupted between p-YC 6 [22]. The direction of Y-dependence in 1 is just the inverse to the case of 4. We call the factor to determine the fine structure of 1 "Ethynyl Influence".
The change in the structures of 1e-g versus those of  (a) The atomic numbering scheme is shown for 1b in Figure 1, as an example The observation is quite different from that in 1, again. The observed structure of 1g is substantially different from that of 6g. Y-dependence in 2 must be very similar to that in 1.
After explanation of the observed structures of 1 in crystals, the role of crystal packing forces is examined in relation to the fine structures of 1.

Crystal Packing Forces as Factor to Determine Fine
Structure of 1. The structures of 1a-c are observed as dimers. Figure 2 shows the dimer formed from 1a, which contains 1a A and 1a B . Se atoms in the 1a dimer are in short contact with C at the 6 position of the partner molecule, and the Se1-C6 distance is 3.392Å. Dimers of 1b and 1c are essentially the same as that of 1a. An Se atom in the 1b dimer is in short contact with C at the 4 position of the partner molecule. The overlap between two naphthyl planes seems larger for the 1b dimer relative to the 1a dimer. The driving force of the dimer formation must be the energy lowering effect by the π-stacking of the naphthyl groups. The π(C) · · · σ * (Se-C sp ) 3c-4e interaction must also contribute to stabilize the dimers. The dimer formation must stabilize the A structure for 1a-c. It would be difficult to conclude whether the structures are A or B without such dimer formation. However, the A structure of 1a-c would be suggested without the aid of the dimer formation by considering the electron affinity of naphthalene (NapH) and the evaluated values for p-YC 6 H 4 CCH (Y = H, OMe, and Me), which are the components of 1.
After the establishment of the structures of 1 and 2 in crystals, next extension is to examine the structures of 1-3 in solutions.  Table 2 collects the substituent induced δδ(H 2 ), δ(H 8 ), and δ(Se) values for 1-3. Table 2 7 (A: pl) and 8 (B: pd).

Behavior of 1−3 in Solutions Based on NMR
To organize the process for the analysis, δ(H 2 : 3) and δ(Se: 3) are plotted versus δ(H 2 : 2) and δ (Se: 2), respectively. Figure 2 shows the plots. The correlations are given in Table 3 (entries 1 and 2, resp.). The correlations are very good (r ≥ 0.995). The results show that the structure of each member in 3 is very close to that of 2, in solutions. Therefore, the structures of 2 should be analyzed from the viewpoint of the orientational effect, together with those of 1. The anisotropic effect of the C ≡C bond in 3 (G = Br) might be stronger than that in 2 (G = Cl), since δ(H 2 ) values of 3 (8.39-8.44) are observed slightly more downfield than those of 2 (8. 30-8.38).
As shown in Table 2 30-8.38. We must be careful when the structures of 1-3 are considered based on δ(H 2 ), since H atoms above the C≡C bond is more deshielded which is just the inverse anisotropic effect by the phenyl group. The magnitudes of the former must be smaller than of the latter. Namely, the structures of 2 and 3 are expected to be B in solutions, although the slight equilibrium between A and B could not be neglected. The structures of 1 would be A in solutions, although A may equilibrate with B to some extent. Figure 4 shows the plots of δ(H 2 : 1 and 2) versus δ (H 1 : 7) and δ (H 2 : 8). The plots appear from downfield to upfield in an order of δ(H 2 : 1) δ (H 2 : 2). The correlations are given in Table 3 (entries 3-6), which support above discussion.
δ(H 8 : 1) and δ(Se: 1) are plotted versus δ(H 1 : 7) and δ (Se: 7), respectively. Figure 5 shows the results. The   correlations are shown in Table 3 (entries 7 and 8, resp.). The correlation of the former is good, which means that (A: pl) contributes predominantly to the structures of 1, although the correlation constant is a negative value of -0.34. The negative value would be the reflection of the inverse anisotropic effect between the phenyl π system and the ethynyl group. It is concluded that the structures of 1 in solutions are substantially (A: pl) with some contributions of (B: pd) and/or (B: pl) through the equilibrium. The correlation for the plot of δ(Se: 1) versus δ(Se: 7) also supports the conclusion, although A is suggested to equilibrate with B in solutions. Indeed, the preferential contribution of B is predicted for 2, but, the plots of δ(H 2 : 2) versus δ(H 2 : 8) do not give good correlations (Panel (b) of Figure 4 and entry 6 in Table 3). Although not shown, the plot of δ(Se: 2) versus   δ(Se: 8) did not give good correlation either (entry 10 in Table 3). The plots of δ(Se: 2) versus δ(Se: 7) gave rather good correlation (entry 9 in Table 3). The discrepancy must come mainly from the equilibrium between (B: pd) and (B: pl). Namely, the structures of 2 are predominantly B, which are in equilibrium between (B: pd) and (B: pl) especially for Y of strong electron accepted groups (Scheme 5). The equilibrium with A would exist but the contribution must be small for most of Y. The B structures of 2 and 3 in solutions are determined based on the large downfield shifts of δ(H 2 : 2) and δ(H 2 : 3) versus δ (H 2 : 1). The reason for the structural determination in solutions will be discussed, next. 13 C-NOE Difference Spectroscopy for 1e and 2e in Solutions. 1e (G = H, Y = Cl) and 2e (G = Y = Cl) were employed for the selective 1 H, 13 C-NOE difference spectroscopy. 13 C NMR spectra were measured for 1e and 2e under the completely 1 H decoupling mode, the offresonance decoupling mode, and the selective 1 H, 13 C -NOE difference mode at the δ(H 2 ) frequency: The atom numbers are shown in Scheme 2. Figure 6 shows the 13 C NMR spectra for 2e. Panels (a)-(c) of Figure 6 correspond to the selective 1 H, 13 C -NOE difference spectroscopy, offresonance decoupling spectroscopy, and completely decoupling spectroscopy, respectively. As shown in Panel (a) of Figure 6, the selective irradiation at the δ(H 2 ) frequency of 2e enhances exclusively the 13 C NMR signals of C 2 and C 9 of 2e, relative to others. On the other hand, only 13 C NMR signal of C 2 of 1e is enhanced relative to others, when the δ(H 2 ) frequency of 1e is selectively irradiated, although not shown. The results must be the reflection of the expectation that H 2 is very close to C 9 in 2e to arise the nuclear interaction resulting in the NOE enhancement, whereas such interaction does not appear between H 2 and C 9 in 1e due to the long distance between them. Namely, structures of 1e and 2e are demonstrated to be A and B, respectively, in solutions on the basis of the homonuclear NOE difference spectroscopy. The structure of 3e must also B in solutions on the analogy of the case in 2e. The results strongly support above conclusion derived from the δ(H 2 ) values of 1-3.

Conclusions
The behavior of ethynylchalcogenyl groups is examined as the factor to control fine structures. The effect is called G-dependence. The G-dependence must arise from the energy lowering effect of the n p (Cl)· · · σ * (Se-C sp ) 3c-4e interaction. The n p (Cl)-π(Nap)-n p (Se)-π(C≡C) interaction may also contribute to stabilize the structure. The structures of 1, 2, and 3 (G = Br) are also examined in solutions based on the NMR parameters for (A: pl) of 9-(arylselanyl)anthracenes (7) and (B: pd) of 1-(arylselanyl)anthraquinones (8). The results show that 2 and 3 behave very similarly in solutions, and the structures of 2 and 3 are predominantly B in solutions with some equilibrium between pd and pl for the aryl groups. The selective 1 H, 13 C-NOE difference spectroscopic measurements strongly support that the structures are A for 1 and B for 2 and 3 in solutions derived from the δ(H 2 ) values of 1-3.