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The intrinsic dynamic and static natures of the E⋯E′ interactions at the 1,8-positions of 1-(MeE)–8-(MeE′)C10H6 [1a–1f (E ≠ E′) and 1g–1j (E = E′)] were elucidated with QTAIM-DFA, after structural determination of 1-(PhE)–8-(PhE′)C10H6 (3a–3f), where (E, E′: x) = (O, S: a), (O, Se: b), (O, Te: c), (S, Se: d), (S, Te: e), (Se, Te: f), (O, O: g), (S, S: h), (Se, Se: i) and (Te, Te: j) (χE ≥ χE′). While the AB structures are confirmed for 3a, 3b and 3d–3f, which consist of the np(E)⋯σ*(E′–CPh) interactions, the structure was BB for 3c, where the E–CR/E′–CR (R = Ph) bond is perpendicular to the naphthyl plane in A and it is placed on the plane in B. While the AB structures are determined by the p(E)–π(Ph) conjugations, the BB structure is by the crystal packing effect. The BA structure with np(E′)⋯σ*(E–CPh) was not detected. While the nature of a typical hydrogen bond with covalency was predicted for BB, AA and BA, with the CT-MC (molecular complex formation through charge transfer) nature for AB in 1e and 1f (R = Me for E–CR/E′–CR), the CT-MC nature was predicted for all conformers of 1j, for example. NBO analysis for 1a–1f revealed that the acceptor orbitals contribute much more than the donor orbitals and the order is σ*(O–CMe

The dynamic and static nature of XH-*-π and YX-*-π in the coronene π-system (π(C24H12)) is elucidated by QTAIM dual functional analysis, where * emphasizes the presence of bond critical points (BCPs) in the interactions. The nature of the interactions is elucidated by analysing the plots of the total electron energy densities Hb(rc) versus Hb(rc) − Vb(rc)/2 [=(ħ2/8m)∇2ρb(rc)] for the interactions at BCPs, where Vb(rc) are the potential energy densities at the BCPs. The data for the perturbed structures around the fully optimized structures are employed for the plots in addition to those of the fully optimized structures. The plots are analysed using the polar coordinate of (R, θ) for the data of the fully optimized structures, while those containing the perturbed structures are analysed using (θp, κp), where θp corresponds to the tangent line of each plot and κp is the curvature. Whereas (R, θ) show the static nature, (θp, κp) represent the dynamic nature of the interactions. All interactions in X–H-*-π(C24H12) (X = F, Cl, Br and I) and Y–X-*-π(C24H12) (Y–X = F–F, Cl–Cl, Br–Br, I–I, F–Cl, F–Br and F–I) are classified by pure CS (closed shell) interactions and are characterized as having the vdW nature, except for X–H = F–H and Y–X = F–Cl, F–Br and F–I, which show the typical-HB nature without covalency. The structural features of the complexes are also discussed.

Invited for this month's cover picture is the group of Dr. Satoko Hayashi at Faculty of Systems Engineering and Chemistry at Wakayama University. The cover picture shows the linear Se(16) σ(16c–30e) interactions, illustrated by the molecular graph type on the optimized structure of the dicationic octamer of 1,5‐(diselena)cane. HOMO‐1 of ψ(462) is drawn on the structure, which is located predominantly on the Se atoms. The optimized structure is stable, due to the nice engagement between the (CH(2))(3) moieties. The contour maps of ρ(r) are also drawn on the molecular C (s) planes of the dicationic dimer and trimer to demonstrate clearly the existence of the interactions between Se atoms. Read the full text of their Full Paper at 10.1002/open.202100017.

Indirect one-bond nuclear spin-spin couplings between M and C [1 J(M,C)] in Me4 M, Me3 M- , Ph4 M, and Ph3 M- (M=Pb, Sn, Ge, Si, C) are analyzed with consideration of the relativistic effect and by employing Slater-type basis sets. The evaluated total values 1 JTL (M,C) reproduced the observed values with some systematic calculation errors. Fermi contact terms 1 JFC (M,C) contribute predominantly to 1 JTL (M,C) (≈99 %). A distinct relativistic effect on 1 J(Pb,C) is predicted for Me3 Pb- and Ph3 Pb- . The mechanisms for the distinct effect are elucidated by using the comparison between Me3 Pb- and Me4 Pb as an example. The contributions to 1 JFC (M,C) [or 1 JSD+FC (M,C), where SD denotes the spin-dipolar term] are decomposed into those of occupied orbitals and occupied-to-unoccupied transitions. The s-type lone-pair orbitals are demonstrated to contribute to the distinct relativistic effect on 1 J(Pb,C) of Me3 Pb- (and Ph3 Pb- ). The results are in sharp contrast to the cases of 1 J(M,C) for M atoms lighter than Pb, such as Si, and are explained by the s character of the M-C bonds. This treatment enables visualization and clear recognition the origin of the nuclear couplings for the species exhibiting a relativistic effect.

The nature ofE2X2σ(4c–6e) of theX-*-E-*-E-*-Xtype is elucidated for 1-(8-XC10H6)E–E(C10H6X-8′)-1′ [(1)E,X= S, Cl; (2) S, Br; (3) Se, Cl; (4) Se, Br] after structural determination of (1), (3) and (4), together with modelA[MeX---E(H)—E(H)---XMe (E= S and Se;X= Cl and Br)]. The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied. The total electron energy densitiesHb(rc) are plottedversus Hb(rc) –Vb(rc)/2 for the interactions at the bond critical points (BCPs; *), whereVb(rc) show the potential energy densities at the BCPs. Data for the perturbed structures around the fully optimized structures are employed for the plots, in addition to those of the fully optimized structures. The plots were analysed using the polar coordinate (R, θ) representation of the data of the fully optimized structures. Data containing the perturbed structures were analysed by (θp, κp), where θpcorresponds to the tangent line of the plot and κpis the curvature. Whereas (R, θ) shows the static nature, (θp, κp) represents the dynamic nature of interactions.E-*-Eare all classified as shared shell (S) interactions for (1)–(4) and as weak covalent (Cov-w) in nature (S/Cov-w). The nature ofpureCS (closed shell)/typical-HB (hydrogen bond) with no covalency is predicted forE-*-Xin (1) and (3),regularCS/typical-HB nature with covalency is predicted for (4), and an intermediate nature is predicted for (2). The NBO energies evaluated forE-*-Xin (1)–(4) are substantially larger than those in modelAdue the shortened length at the naphthalene 1,8-positions. The nature ofE2X2of σ(4c–6e) is well elucidatedviaQTAIM-DFA.

Dynamic and static nature of intramolecular π-π interactions between ethylene moieties in diethenodihydronaphthanaphtalene (1 b) and derivatives (2 b–12 b) are elucidated by employing QTAIM-DFA (QTAIM dual functional analysis). During the course of the investigations, doubly degenerated bond paths were detected between carbon atoms in opposite benzene rings of dibenzo-derivative of 1 b with an etheno-bridge on the backside (11 b). It must be very curious, since one BP should correspond to an interaction between two carbon atoms. Intramolecular π-π interactions in 1 b–12 b are all classified by the pure CS (closed shell) interactions. The interactions between ethylene groups, with no substituents as in 1 b–8 b, are predicted to have the van der Waals (vdW) nature. Those for 9 b–12 b have the hydrogen bond (HB) nature with no covalency, where the ethylene moieties are included in one or two benzene ring(s), except for 10 b, if evaluated with MP2/6-311G(3d). The character in 10 b is close to the borderline area between the vdW and HB nature with no covalency, although should be the vdW type. The interactions in 2 b–12 b evaluated with MP2/6-311G(3d) are predicted to be somewhat stronger than the case with MP2/6-311G(d), as a whole.

The nature of EH2-*-π(C14H10) interactions (E = O, S, Se and Te) of an anthracene system was elucidated by applying QTAIM dual functional analysis (QTAIM-DFA) after clarification of the structural features with quantum chemical (QC) calculations. π-HB (hydrogen bond) interactions were detected for E = O, S, Se and Te, whereas π-EB (chalcogen bond) interactions were observed for E = O in (EH2)-*-π(C14H10), where the bond paths connected H in EH2 to C14H10 in π-HB, and they connected E in EH2 to C10H8 in π-EB. The QTAIM-DFA parameters of (R, θ) and (θp, κp) were evaluated for the interactions via analysing the plots of Hb(rc) versus Hb(rc) − Vb(rc)/2 for the interactions at the bond critical points. Data obtained from the perturbed structures around the fully optimized structures were employed for the plots, in addition to the fully optimized structures. Data obtained from the fully optimized structures were analysed using (R, θ), which corresponded to the static nature, and those obtained from the perturbed structures were analysed using (θp, κp), which represented the dynamic nature of the interactions, where θp corresponds to the tangent line of the plot and κp is the curvature. The θ and θp values are less than 90° for all the interactions examined, except for the iH-*-11C(π) interaction in TeH2-*-C14H10 (C1: IIBAtc), where iH is located closer to the centre of C14H10. Therefore, the interactions examined were predicted to have vdW nature, appeared in the pure-CS (closed shell) interaction region, although iH-*-11C(π) was predicted to have the pure-CS/typical-HB nature without covalency. Additionally, the π-HB interaction seems to be slightly stronger than π-EB in (OH2)-*-π(C14H10).

The intrinsic dynamic and static nature of intramolecular OH–*–π interactions is elucidated using a QTAIM dual functional analysis (QTAIM-DFA) after clarifying the structural features. Asterisks (*) are employed to emphasize the presence of bond critical points (BCPs) on the bond paths (BPs), which correspond to the interactions in question. Data from the fully optimized structures correspond to the static nature of the interactions. In our treatment, data from the perturbed structures, which are based around the fully optimized structure, are employed for the analysis in addition to those from the fully optimized structure, which represent the dynamic nature of the interaction. Seven intramolecular OH–*–C(π) interactions were detected in six-membered rings, with six BPs and BCPs for each, among the 72 conformers of the species examined here (1–15). The interactions are predicted to have a vdW or t-HBnc (typical hydrogen bonds with no covalency) nature, which appeared in the pure closed shell region. They appear to be stronger than the corresponding intermolecular interactions. Nine BPs with BCPs were also detected for the intramolecular O–*–X interactions (X = C(π) and H(π), joined to C(π)) in the 5–7-membered rings. The E(2) values of the interactions, as obtained by NBO, are discussed in relation to the stabilities of the conformers and the BPs with BCPs.

The intrinsic dynamic and static nature of G–*–E–*–Y σ(3c–4e) interactions was elucidated with the quantum theory of atoms in molecules dual functional analysis (QTAIM-DFA), employing o-MenGCH2C6H4EY (MenG = Me2N and MeE; E = O, S, Se and Te; Y = F, Cl, Br, I, EMe and Me). Asterisks (*) are employed to emphasize the existence of bond critical points (BCPs) on the bond paths (BPs), corresponding to the interactions in question. Data from the fully optimized structure correspond to the static nature of interactions. The dynamic nature is called the intrinsic dynamic nature if the perturbed structures are generated using the coordinates derived from the compliance constants. Basis sets of the Sapporo-TZP type with diffusion functions are employed for the heteroatoms at the MP2 level. The noncovalent G–*–E interactions in GEY σ(3c–4e) are predicted to demonstrate van der Waals bonding to CT-TBP (trigonal bipyramidal adduct formation through charge transfer) nature, while the E–*–Y bonds have the covalent nature. Some E–F bonds show strong ionic character when G–*–E is predicted to be stronger than E–*–Y. The contributions of the CT terms to the G–*–E interactions, evaluated with NBO, are discussed in relation to the predicted nature. The E(2) values based on NBO are strongly correlated to the compliance constants for the G–*–E interactions if suitably treated separately.

The nature of extended hypervalent interactions of the BE–*–AE–*–AE–*–BE type is elucidated for 1-(8-MeBEC10H6)AE–AE(C10H6BEMe-8′)-1′, (1 (AE, BE) = (S, S), 2 (S, Se), 3 (Se, S) and 4 (Se, Se)) and models A–D, BR2BE⋯(AR)AE–AE(AR)⋯BEBR2 (AR, BR = H and Me). QTAIM dual functional analysis, which we proposed recently, is applied to the analysis. Total electron energy densities Hb(rc) are plotted versus Hb(rc) − Vb(rc)/2 for the interactions at bond critical points (BCPs; *), where Vb(rc) show potential energy densities at BCPs. Data for the perturbed structures around the fully optimized structures are employed for the plots, in addition to those of the fully optimized ones. While the data for the fully optimized structures are analysed by the polar coordinate (R, θ) representation, those containing the perturbed structures are by (θp, κp): θp corresponds to the tangent line for the plot and κp is the curvature. While (R, θ) show the static nature, (θp, κp) represent the dynamic nature of interactions. All AE–*–AE interactions in 1–4 and models A–D are classified by the shard shell interactions and have the character of a weak covalent nature. The AE–*–BE interactions in 1–4 are all classified by the regular closed shell interactions. They are predicted to have the typical HB (hydrogen bond) nature with covalency for 1 and 2 but the nature of the molecular complex formation through CT for 3 and 4. The AE–*–BE interactions in models A–D are predicted to be weaker than those in 1–4.

The nature of the π–interactions in the 1 : 1 and 2 : 1 adducts of EH2 with the naphthalene π-system (E = O, S, Se and/or Te) is elucidated by applying QTAIM-DFA (QTAIM dual functional analysis). The H–*–π interactions are detected in EH2–*–π(C10H8) and (EH2)2–*–π(C10H8) for E = S, Se and Te, whereas E–*–π interactions are in OH2–*–π(C10H8), (OH2)2–*–π(C10H8) and HE–H–*–π(C10H8) (denoted by HHE–*–C10H8) (E = S, Se and Te). Asterisks * emphasize the existence of bond critical points (BCPs) on the interactions in question. Hb(rc) are plotted versus Hb(rc) − Vb(rc)/2 at the BCPs in QTAIM-DFA. Plots for the fully optimized structures are analyzed using the polar coordinate (R, θ) representation. Those containing the perturbed structures are by (θp, κp): θp corresponds to the tangent line of the plot and κp is the curvature. While (R, θ) describe the static nature, (θp, κp) represent the dynamic nature of interactions. The θ and θp values are less than 90° for all interactions in question, examined in this work, except for θp = 90.6° for HHTe–*–π(C10H8). Therefore, all interactions examined are classified by the pure-CS (closed shell) interactions and predicted to have vdW-nature, except for HHTe–*–π(C10H8), which should have the character of the typical HB-nature without covalency. The π–EB interaction in HHS–*–C10H8 is predicted to have the border character between the vdW-nature and the typical HB-nature without covalency, since θp = 89.8°. The nature of four interactions appeared between 2H in TeH2 and C10H8 in TeH2–*–π(C10H8) is also clarified well using QTAIM-DFA.

The nature of the transannular E-∗-E' interactions in neutral, radical cationic, and dicationic forms of cyclo-E(CH2CH2CH2)2E' (1) (E, E' = S, Se, Te, and O) (1, 1(•+), and 1(2+), respectively) is elucidated by applying QTAIM dual functional analysis (QTAIM-DFA). Hb(rc) are plotted versus Hb(rc) - Vb(rc)/2 for the data of E-∗-E' at BCPs in QTAIM-DFA, where ∗ emphasizes the existence of BCP. Plots for the fully optimized structures are analyzed by the polar coordinate (R, θ) representation. Those containing the perturbed structures are by (θp, κp): θp corresponds to the tangent line of the plot, and κp is the curvature. While (R, θ) describes the static nature, (θp, κp) represents the dynamic nature of interactions. The nature is well-specified by (R, θ) and (θp, κp). E-∗-E' becomes stronger in the order of 1 < 1(•+) < 1(2+), except for O-∗-O. While E-∗-E' (E, E' = S, Se, and Te) in 1(2+) are characterized as weak covalent bonds, except for S-∗-Te (MC nature through CT) and Se-∗-Te (TBP nature through CT), O-∗-E' seems more complex. The behavior of E-∗-E' in 1(2+) is very close to that of cyclo-E(CH2CH2CH2)E' (E, E' = S, Se, Te, and O), except for O-∗-O.

Atoms-in-molecules dual functional analysis (AIM-DFA) is applied to the E–E′ bonds (E, E′ = S and Se) in R-cystine (1) and the derivatives of 1, together with MeEE′Me. Hb(rc) are plotted versus Hb(rc) − Vb(rc)/2 at bond critical points (BCPs), where Hb(rc) − Vb(rc)/2 = (ħ2/8m)∇2ρb(rc). The plots are analyzed by the polar coordinate (R, θ) representation. Data of perturbed structures around the fully optimized structures are also plotted in this treatment. Perturbed structures are generated using NIV (normal coordinates of internal vibrations). Each plot for an interaction with data of a fully optimized and four perturbed structures gives a curve, which supplies important information. It is expressed by (θp, κp): θp corresponds to the tangent line for the plot measured from the y-direction and κp is the curvature. While (R, θ) correspond to the static nature of interactions, (θp, κp) represent the dynamic nature. The behavior of the E–E′ bonds is well described by (R, θ) and (θp, κp).

The dynamic and static nature of extended hypervalent interactions of the BE···AE···AE···BE type are elucidated for four center–seven electron interactions (4c–7e) in the radical cationic dimers (1·+) and 4c–6e in the dicationic dimers (12+) of 1,5-(dichalcogena)canes (2: AE(CH2CH2CH2)2BE: AE, BE = S, Se, Te, and O). The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied for the analysis. Total electron energy densities Hb(rc) are plotted versus Hb(rc) – Vb(rc)/2 [= (ℏ2/8m)∇2ρb(rc)] at bond critical points (BCPs) of the interactions, where Vb(rc) values show potential energy densities at BCPs. Data from the fully optimized structures correspond to the static nature of the interactions. Those from the perturbed structures around the fully optimized ones are also plotted, in addition to those of the fully optimized ones, which represent the dynamic nature of interactions. The BE···AE–AE···BE interactions in 12+ are stronger than the corresponding ones in 1·+, respectively. ...

The nature of the E-*-E' bonds in neutral, monoanionic, monocationic, and dicationic forms of HEE'H (1), MeEE'Me (2), and cyclo-1,2-EE'(CH2)3 (3) (E, E' = O, S, Se, Te) is investigated by applying AIM (atoms-in-molecules method) dual functional analysis. Hb(rc) are plotted versus Hb(rc) – Vb(rc)/2 for the data of E-*-E' at bond critical points (BCPs) of fully optimized structures and perturbed structures around the fully optimized ones. Plots for the fully optimized structures are analyzed by the polar coordinate (R, θ) representation. The (θp, κp) parameters are derived from those of the perturbed structures: θp corresponds to the tangent line of each plot, and κp is the curvature. While (R, θ) correspond to the static nature, (θp, κp) represent the dynamic nature of interactions. The nature of E-*-E' in the neutral and charged species is classified by comparing their θ and θp values with those of the standard interactions as a reference. Data for E-*-E' in the neutral forms of 1–3 appear in the shared-shell (SS) region (180° < θ), except for MeS-*-TeMe (2c), which does in the regular closed-shell (CS) region (90° < θ < 180°). The E–E' bonds in the monoanionic forms of 1–3 become much longer and weakened. Therefore, data of the monoanionic forms appear in the regular CS. On the other hand, the strengths of E-*-E' in the mono- and dicationic forms are almost equal to those in the neutral forms of 1–3 in the plots, irrespective of the shorter E-*-E' lengths in the cationic forms, relative to the neutral forms.

Compound (2-MeOC6H4CS)2S (1) showed an unusual saddle structure in which the –C(=S)–S–C(=S)– moiety is planar and two benzene rings lie a face-to-face and the distances (3.07 A) between the central sulfur atom and two 2-methoxy oxygen atoms are within the sum of van der Waals radii of the both atoms. However, the results of MO calculation at the B3LYP/6-311+G(2d, p) level showed no orbital interaction between both atoms. From the results of the calculations at the MP2 level, it was deduced that the crystal packing effect is important for such densely packed crystal, due to its less effective volume. On the other hand, the para-methoxy derivative (4-MeOC6H4CS)2S (2) in which the two methoxy oxygen atoms are not able to contact with the central sulfur atom shows an L-shaped structure in which the –C(=S)–S–C(=S)– moiety is not planar. The –C(=O)–S–C(=S)– moiety in compound (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b) shows an L-shaped structure, though the two methoxy oxygen atoms are in intramolecular contact with the central sulfur atom. The deep blue to green colors of compounds 1 and 2 and the deep violet color of compound 3b are due to transitions of the lone-pair electrons in the HOMO (ψ87) of the thiocarbonyl sulfur atom to the LUMO (ψ89)and of those in the HOMO (ψ83) of the thiocarbonyl sulfur atom to the LUMO (ψ85), respectively.

The structure of 2-(2-pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine (NSN) indicates that the molecule has a planar geometry with a linear N···S···N linkage, creating a tetracyclic structure of the formal C2v symmetry. To clarify the nature of the NSN σ(3c–4e) bonding, together with the related NSeN and NTeN, the dynamic and static behaviors are investigated by applying atoms-in-molecules (AIM) dual functional analysis to both the fully optimized and perturbed structures. The structures were optimized computationally, retaining C2v symmetry. All bond critical points are detected as expected and exhibited on both sides of the N···Z···N moiety which supports the formation of NZN σ(3c–4e). It is confirmed that N···S···N is of the covalent nature close to Me2S+-∗-Cl or Me2Se+-∗-Br, whereas N···Se···N and N···Te···N have the (regular) CS nature close to the CT adducts of Me2S(-∗-Cl)2 (TBP) and Me2Se-∗-Br2 (MC), respectively. An experimental high-resolution charge density determination has been performed on ...

The p(Z)–π(Ar) conjugation as the factors to control the fine structures of organic chalcogen compounds are investigated. The structures of 1-(arylchalcogena)naphthalenes [1-(p-YC6H4Z)C10H7, 1-ArZNap; 1 (Z = O) and 2 (Z = S)] are determined by the X-ray crystallographic analysis. The structures of 1, 2, and 1-ArTeNap (4) are also determined in solutions, together with 1-ArSeNap (3), employing the NMR data of 9-(arylselanyl)anthracenes (5) and 1-(arylselanyl)anthraquinones (6). NMR data of 5 and 6 can be used as the standard of the A and B structures, respectively, for all Y examined in solutions: The Se–CAr bond in 5 (A) is placed almost perpendicular to the anthryl plane in A, and the bond is located on the plane in 6 (B). Structures of 1–4 are A if Y are electronically accepting groups such as Y = Cl, but they are B with Y of donating groups such as Y = OMe both in crystals and solutions. It is interesting that δ(Ci: 1–4) are hardly affected from the conformation around the Z–CAr bonds, whereas δ(H: 1–4...

Mechanisms operating in weak interactions are sometimes quite different from those in strong ones. Factors to control the non-bonded G···Z (Z = O, S, and Se) distances at naphthalene 1,8-positions in 8-G-1-RZC 10 H 6 are analyzed as an example to clarify the causality of weak interactions. Structures around Z in 8-G-1-RZC 10 H 6 are well explained by three types, A, B, and C, where the Z―CR bond is perpendicular to the naphthyl plane in A, it is placed on the plane in B, and C is intermediate between A and B. The r(Z...Z) distances in 1,8-(RZ) 2 C 10 H 6 are observed to increase in an order of BB < CC < AB < AA. It seems difficult to explain the sequence based on the magnitudes of the closed-shell Z···Z interactions, since the BB interaction must not be so strong especially for Z of heavier atoms. The mechanism to control the r(Z···Z) distances is demonstrated to be the reflection from the repulsive interactions between R and H at the 2-position in 1,8-(RZ) 2 C 10 H 6 . Similar phenomena are also detected in the observed and calculated results at the benzene 1,2-, anthracene 1,8,9-, and anthraquinone 1,8,9-positions, which are explained based on the mechanism. Proposed idea and mechanism will help us to understand what happens in such weak interactions.

The p(Z)-pi(Ar) conjugations must operate fully in the ground states of 9-(arylchalcogenyl)triptycenes (p-YC(6)H(4)ZTpc:1 (Z = O), 2 (Z = S), 3 (Z = Se), and 4 (Z = Te)), where the p-YC(6)H(4) group is placed in the bisected area between two phenyl planes of the triptycyl group with the parallel orientation. The ground-state geometries, which we call (A: pl), are confirmed by X-ray analysis. However, the conjugations never operate in the transition states between (A: pl) and/or the topomeric structures (A': pl'), where the Z-C(Tpc) bond is perpendicular to the plane. The site-exchange processes correlate to the conjugations. Temperature-dependent (1)H NMR spectra are analyzed for 2 and 3 to demonstrate the effective p(Z)-pi(Ar) conjugations. The activation energies for the interconversion between (A: pl) and (A': pl') (GR: gear process) were obtained for 2 (DeltaG(GR)(2)) and 3 (DeltaG(GR)(3)). DeltaG(GR)(3) correlate well with DeltaG(GR)(2), and DeltaG(GR)(2) are well analyzed by the Hammett-type dual parameters. DeltaG(GR)(2) and DeltaG(GR)(3) are demonstrated to be controlled by the resonance interaction of the p(Z)-pi(C(6)H(4))-p(Y) conjugations. QC calculations are performed on the ground and exited states of 1-4, which clarify the effective p(Z)-pi(C(6)H(4))-p(Y) conjugations for Z of heavier atoms.

77Se NMR chemical shifts of methyl-d 3 derivatives of 8-methyl-1-(phenylselanyl) naphthalene ( 1 ) and 8-methyl-1-(p-anisylselanyl)naphthalene ( 2 ) are observed 0.25 and 0.20 ppm upfield from 1 and 2 , respectively. The observations must be the reflection of the nonbonded interactions of the C─H—Se 3c–4e type in 1 and 2 . The mechanism is elucidated by means of crystallographic and theoretical investigations. The nonbonded distance between Se and C Me (2.989 A) is observed to be shorter than the sum of the van der Waals radii of the two by 0.91 A in 2 . 1 and 2 may be in equilibrium between conformers A and B in solution, where Se─C i is perpendicular to the naphthyl plane in A and it is on the plane in B . Natural bond orbital (NBO) analysis on 1 revealed that the nonbonded n p (Se)—σ *(C─H) interaction contributes in A , whereas nonbonded n s (Se)—σ *(C─H) and double σ (C─H)—σ *(Se–C) interactions operate in B .

Bis-selenides(LL), such as 8-[MeSe(X)]-1-[MeSe(Z)]C10H6 (1(LL)), 8-[EtSe(X)]-1-[EtSe(Z)]C10H6 (2(LL)), 8-[p-YC6H4Se(X)]-1-[MeSe(Z)]C10H6 (3(LL)) and 8-[p-YC6H4Se(X)]-1-[p-YC6H4Se(Z)]C10H6 (4(LL)) were oxidized with ozone at 0 °C, where (X, Z) = (lone pair, lone pair) for LL. Bis-selenoxides, 1(OO), 3(OO) and 4(OO) where (X, Z) = (oxygen, oxygen), were obtained in the oxidation of 1(LL), 3(LL) and 4(LL), respectively, via corresponding selenide-selenoxides, 1(LO), 3(LO) and 4(LO), respectively. A facile Se–C bond cleavage was observed in 2(LL). The structures of 1(LO) and 1(OO) were determined by the X-ray analysis. Three Se⋯SeO atoms in 1(LO) and four OSe⋯SeO atoms in 1(OO) align linearly. While the non-covalent Se⋯SeO 3c–4e interaction operates to stabilize 1(LO), the non-covalent OSe⋯SeO 4c–4e interaction would not stabilize 1(OO). The 3c–4e interaction must play an important role to control the stereochemistry of selenoxides. The 8-G-1-[MeSe(OH)2]C10H6 (n(OH·OH)) are the key intermediates in the racemization of 8-G-1-[MeSe(O)]C10H6 (n(O)) in solutions, where G = SeMe (1), H (5), F (6), Cl (7) and Br (8). Energies of n(OH·OH), relative to n(O), are evaluated based on the theoretical calculations. G of SeMe is demonstrated to operate most effectively to protect from racemization of selenoxides among n = 1 and 5–8, since the relative energies for G of cis- and trans-SeMe are largest.

Fine structures of 8-G-1-(p-YC6H4C ≡ CSe)C10H6[1(G = H) and2(G = Cl): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f), andNO2(g)] are determined by the X-ray analysis. Structures of1,2, and3(G = Br) are calledAif each Se–Cspbond is perpendicular to the naphthyl plane, whereas they areBwhen the bond is placed on the plane. Structures are observed asAfor1a–cbearing Y of nonacceptors, whereas they areBfor1e–gwith Y of strong acceptors. The change in the structures of1e–gversus those of1a–cis called Y-dependence in1. The Y-dependence is very specific in1relative to 1-(p-YC6H4Se)C10H7(4) due to the ethynyl group: the Y-dependence in1is almost inverse to the case of4due to the ethynyl group. We call the specific effect “Ethynyl Influence.” Structures of2are observed asB: theA-type structure of1bchanges dramatically toBof2bby G = Cl at the 8-position, which is called G-dependence. The structures of2and3are examined in solutions based on the NMR parameters.

Homonuclear Z···Z (Z=O, S, Se, and Te) interactions are investigated employing naphthalene 1,8-positions in 1,8-(MeZ)2C10H6 (1a–1d: Z=O (a), S (b), Se (c), and Te (d)), 1-MeZ-8-PhZC10H6 (2a–2c), an...

8-G-1-(p-YC6H4C CSe)C10H6 [2 (G = Cl) and 3 (G = Br): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f) and NO2 (g)] have been prepared and the NMR spectra measured, in addition to 1 (G = H). Structures have been determined by X-ray crystallographic analysis for 2b, 2e and 2g, which are all type B (B), where the Se–Csp bond is placed in the naphthyl plane in B. The type is classified as A if the Se–Csp bond is perpendicular to the naphthyl plane. Structures around the p-YC6H4 (Ar) group are pd (perpendicular) for Y = OMe (2b) and Cl (2e) and pl (planar) for Y = NO2 (2g), where the Se–CNap bond is placed in the aryl plane in pl and perpendicular to the plane in pd. The 1b (A: pd) structure changes dramatically on going to 2b (B: pd) with G = Cl at the 8-position. The effect is called the G-dependence in 2. The G-dependence arises from the energy lowering effect of the np(Cl)⋯σ∗(Se–Csp) 3c–4e interaction. Structures are both (B: pd) for 1e and 2e and both (B: pl) for 1g and 2g. One may realize that the structures are unchanged by G = Cl in place of G = H for Y = Cl and NO2 at a first glance. However, the B structures in 2e and 2g must be much more stabilized by the G-dependence of the np(Cl)⋯σ∗(Se–Csp) 3c–4e interaction or the G⋯Se–Csp–Csp–Csp2 5c–6e type interaction. The structures of 2 and 3 are examined in solution based on the NMR parameters. The results show that 2 and 3 behave very similarly to each other and the structures are predominantly B, with some equilibrium between pd and pl around the aryl groups in solution. Quantum chemical calculations support the observations.

A set of new delta(Se) parameters is proposed as a standard for the planar (pl) orientational effect of p-YC(6)H(4) (Ar) in ArSeR, employing 9-(arylselanyl)triptycenes (1: p-YC(6)H(4)SeTpc). The Se-C(R) bond in ArSeR is placed on the Ar plane in pl and it is perpendicular to the plane in pd. Large upfield shifts are observed for Y = NMe(2), OMe, and Me (-22 to -6 ppm) and large downfield shifts for Y = COOEt, CN, and NO(2) (19-37 ppm), relative to Y = H, with small upfield and moderate downfield shifts by Y of halogens (-1 ppm for Y = F and 4 ppm for Y = Cl and Br). This must be the result of the p(Se)-pi(C(6)H(4))-p(Y) conjugation in 1 (pl). While the character of delta(Se) in 1 (pl) is very similar to that in 9-(arylselanyl)anthracenes (2 (pl)), it is very different from that of 1-(arylselanyl)anthraquinones (3 (pd)). Sets of delta(Se) of 1 and 2 must serve as the standard for pl and that of 3 does for pd in solutions. Structures of various ArSeR in solutions are determined from the viewpoint of the orientational effect based on the standard delta(Se) of 1-3. While the structure of 2-methyl-1-(arylselanyl)naphthalenes is concluded to be all pl in solutions, those of 8-chloro- and 8-bromo-1-(arylselanyl)naphthalenes are all pd, except for Y = COOEt, CN, and NO(2): The equilibrium between pd and pl contributes to those with Y = COOEt, CN, and NO(2). The structure of 1-(arylselanyl)naphthalenes changes depending on Y. The structures of ArSeMe and ArSeCOPh are shown to be pl and pd, respectively, in solutions. Those of ArSePh and ArSeAr seem to change depending on Y. delta(Se) of 1-3 are demonstrated to serve as the standard to determine the structures in solutions. The rules of thumb derived from the characters in delta(Se) for 1-3 are very useful to determine the structures of ArSeR in solutions, in addition to the analysis based on the plots.

Contributions from atomic p(Se), d(Se), and f(Se) orbitals to sigmap(Se) are evaluated for neutral and charged Se*Hn (*=null, +, or -) and some oxides to build the image of the contributions. The effect of methyl and halogen substitutions is also examined employing RrSe*XxOo (*=null, +, or -) where R=H or Me; X=F, Cl, or Br. The p(Se) contributions are larger than 96 % for SeH- (Cinfinityv), SeH2 (C2v), SeH3 + (C3v), SeH3 + (D3h), and SeH4 (Td). Therefore, sigmap(Se) of these compounds can be analyzed based on p(Se). The p(Se) contributions are 79-75 % for SeH4 (TBP), SeH5 + (TBP), SeH5 + (SP), and SeH5 - (SP). Methyl and halogen substitutions increase the contributions by 1-2 % (per Me) and 4-7 % (per X), respectively. The contributions are 92-79 % for H2SeO (Cs), H2SeO2 (C2v), and H4SeO (C2v). The values are similarly increased by the substitutions. Consequently, sigmap(Se) of these compounds can be analyzed based on p(Se) with some corrections by d(Se). The p(Se) contribution of SeH6 (Oh) is 52 %: sigmap(Se: SeH6 (Oh)) must be analyzed based on both p(Se) and d(Se). The contributions for the Me and X derivatives of SeH(6) amount to 86-77 %. Therefore, sigmap(Se) of the derivatives can also be analyzed mainly based on p(Se) with some corrections by d(Se). Contributions from f(Se) are negligible. Contributions from 4p(Se) in vacant orbitals are also considered. A utility program derived from the Gaussian 03 (NMRANAL-NH03G) is applied to evaluate the contributions.

Electron population terms are evaluated for N=Se, S, and O. Calculations are performed on HOMO and LUMO constructed by pure atomic 4p(Se), 3p(S), and 2p(O) orbitals, employing the 6-311+G(3d) and/or 6-311(++)G(3df,3pd) basis sets at the HF, MP2, and DFT (B3 LYP) levels. Se(4+), Se(2+), Se(0), and Se(2-) with the O(h) symmetry are called G(A: Se) and HSe(+), H(2)Se, and HSe(-) with the C(infinityh) or C(2v) symmetry are named G(B: Se), here [G(A+B: Se) in all]. HOMO and LUMO in G(A+B: N) (N=Se, S, and O) satisfy the conditions of the calculations for . The (4p), (3p), and (2p) values correlate well with the corresponding MO energies (epsilon(N)) for all calculation levels employed. Plots of (HOMO) and (LUMO) versus Q(N) (N=Se, S, and O) at the HF and MP2 levels are analyzed as two correlations. However, the plots at the DFT level can be analyzed as single correlation. A regression curve is assumed for the analysis. Behaviors of clarify how valence orbitals shrink or expand depending on Q(N). The applicability of is examined to establish a new method that enables us to analyze chemical shifts with the charge effect separately from others. A utility program derived from the Gaussian 03 (NMRANAL-NH03G) is applied to evaluate and examine the applicability to the NMR analysis.

The origin of δ (Se) is revealed based on the MO theory. The pre-α effect in H 2 Se, defined in the text, is the generation of double σ(Se─H) and σ*(Se─H) through the protonation to spherical Se 2− . The extension of HOMO-n (n = 0, 1, and 2) over the whole molecule of Me 2 Se is mainly responsible for the α effect. The β effect originates not from the occupied-to-unoccupied transitions but from the occupied-to-occupied transitions. The γ effect of the upfield shifts is the results of the subtle balance between two types of transitions. Contributions from each MO (ψ i ) and each ψ i → ψ a transition are evaluated separately, using a utility program (NMRANAL-NH03G).

Two sets of delta(H) and delta(C) are proposed by employing 9-(arylselanyl)anthracenes [9-(p-YC6H4Se)Atc: 1] and 1-(arylselanyl)anthraquinones [1-(p-YC6H4Se)Atq: 2] with various Y's. Structures of 1 and 2 are (A: pl) and (B: pd), respectively, for all Y examined in chloroform-d. After elucidation of the behavior of delta(H, C: 1) and delta(H, C: 2), they are applied to determine the structures in chloroform-d solutions for 1-(arylselanyl)naphthalenes (3), 1-(arylselanyl)-2-methylnaphthalenes (4), and 1-(arylselanyl)-8-bromonaphthalenes (5). Although the structure of 4 remains in (A: pl) in the solutions for all Y examined, that of 5 is (B: pd), except for Y = CN and NO2. On the other hand, 3 is shown to equilibrate between (A: pl) and (B: pd). Although the contributions of (B: pd) and (A: pl) are predominant for Y = NMe2 and NO2, respectively, the equilibrium constants change from Y to Y in the solutions. The results are supported by the quantum chemical calculations, containing the solvent effect of chloroform. These results demonstrate that delta(H, C: 1) and delta(H, C: 2), as well as delta(Se), serve as the practical standards for pl and pd, respectively, to analyze the structures of p-YC6H4ZR (Z = Se) in solutions.

Plain rules founded in a theoretical background are presented that can be used to determine the structure of selenium compounds on the basis of delta(Se) data and to predict delta(Se) data from a given structure with satisfactory accuracy. As a first step to establish such rules, the origin of delta(Se) is elucidated on the basis of MO theory. The Se(2-) ion was chosen as the standard for the analysis. The concept of the pre-alpha effect is proposed, which is defined as the downfield shift due to protonation of a lone-pair orbital of Se. The pre-alpha effect of two protons in H(2)Se is explained by the generation of double sigma(Se--H) and sigma*(Se--H) through protonation of the spherical Se(2-) ion. The orbitals, together with n(p)(Se), result in effective transitions for the pre-alpha effect. The alpha effect is the downfield shift caused by the replacement of Se--H by Se--Me. The extension of HOMO-2 [4p(y)(Se)], HOMO-1 [4p(x)(Se)], and HOMO [4p(z)(Se)] over the whole Me(2)Se molecule is mainly responsible for the alpha effect. The beta effect originates not from the occupied-to-unoccupied (psi(i)-->psi(a)) transitions but from the occupied-to-occupied (psi(i)-->psi(j)) transitions. Although psi(i)-->psi(j) transitions contribute to upfield shifts in Me(2)Se, the magnitudes become smaller as the methyl protons are substituted by Me groups one after another. The gamma effect of upfield shifts is also analyzed, although complex. The effect of p(Se)-pi(C==C) conjugation is analyzed in relation to the orientational effect. Contributions from each MO (psi(i)) and each psi(i)-->psi(a) transition are evaluated separately, by using a utility program derived from the Gaussian 03 program suite (NMRANAL-NH03G). The treatment enables us to visualize and understand the origin of (77)Se NMR chemical shifts.

The energy profile of 8-(methylselanyl)-1-(methylseleninyl)naphthalene ( 1 ) is revealed to clarify how the Se(O)Me and SeMe groups control the stereochemistry of 1 , through the nonbonded Se–Se O interaction. Six stable structures (SSs) and eight transition states (TSs) are optimized for 1 . Frequency analysis is carried out for all SSs and TSs. The global minimum of 1 is the trans -form of 1 ( 1 ( t - AA )), which reproduces the structure determined by the X-ray crystallographic analysis. Three Se–Se O atoms in 1 ( t - AA ) are on the naphthyl plane and two Me groups are in trans . Next stable one is the cis -form ( 1 ( c - AC ′)). Motions in the imaginary frequencies of six TSs correspond to the rotation around an Se C Nap bond, whereas those of the two to the simultaneous rotations around the two Se C Nap bonds. Attractive interactions must play an important but additional role in the simultaneous rotations in TS. The observed structure in 1,8-bis(methylseleninyl)naphthalene ( 2 ) is also reproduced by the global minimum, where the four O Se–Se O atoms align linearly. NBO analysis reveals that σ (3c–4e) of the nonbonded Se–Se O interaction controls the structure of 1 whereas σ (4c–4e) of the O Se–Se O interaction will not in 2 .

To clarify the nature of five-center, six-electron (5c-6e) C 2 Z 2 O interactions, atoms-in-molecules (AIM) analysis has been applied to an anthraquinone, 1,8-(MeZ) 2 ATQ (1 (Z=Se), 2 (Z=S), and 3 (Z=O)), and a 9-methoxyanthracene system, 9-MeO-1,8-(MeZ) 2 ATC (4 (Z=Se), 5 (Z=S), and 6 (Z=O)), as well as 1-(MeZ)ATQ (7 (Z=Se), 8 (Z=S), and 9 (Z=O)) and 9-MeO-1-(MeZ)ATC (10 (Z=Se), 11 (Z=S), and 12 (Z=O)). The total electronic energy density (H b (r c )) at the bond critical points (BCPs), an appropriate index for weak interactions, has been examined for 5c-6e C 2 Z 2 O and 3c-4e CZO interactions of the n P (O)···σ*(Z-C) type in 1-12. Some hydrogen-bonded adducts were also re-examined for convenience of comparison. The total electronic energy densities varied in the following order: O···O (3: H b (r c )=0.0028 au)=O···O (6: 0.0028 au) > O···O (9: 0.0025 au)≥ NN···HF (0.0024 au)≥ O···O (12: 0.0023 au) » H 2 O···HOH (0.0015 au) > S···O (8: 0.0013 au) = S···O (2: 0.0013 au) ≥ S···O (11: 0.0012 au) = S···O (5: 0.0012 au)>HF···HF (0.0008 au)=Se···O (10: 0.0008 au) = Se···O (4: 0.0008 au) > Se···O (1: 0.0007 au)≥Se···O (7: 0.0006 au)» HCN···HF (-0.0013 au). H b (r c ) values for S···O were predicted to be smaller than the hydrogen bond of H 2 O···HOH and H b (r c ) values for Se···O are very close to or slightly smaller than that for HF···HF in both the ATQ and 9-MeOATC systems. In the case of Z= Se and S, H b (r c ) values for 5c-6e C 2 Z 2 O interactions are essentially equal to those for 3c-4e CZO if Z is the same. The results demonstrate that two n p (O)···σ*(Z-C) 3c-4e interactions effectively connect through the central n p (O) orbital to form the extended hypervalent 5c-6e system of the σ*(C-Z)···n p (O)···σ*(Z-C) type for Z=Se and S in both systems. Natural bond orbital (NBO) analysis revealed that n s (O) also contributes to some extent. The electron charge densities at the BCPs, NBO analysis, and the total energies calculated for 1-12, together with the structural changes in the PhSe derivatives, support the above discussion.

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.

The orientational effect of p-YC 6 H 4 (Ar) on 6(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. The effect is examined in the cases in which Se-C R in ArSeR is either in the Ar plane (pl) or is perpendicular to the plane (pd). 9-(Arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquionones (2) are employed to establish the effect in pl and pd, respectively. Large upfield shifts are observed for Y=NMe 2 , OMe, and Me, and large downfield shifts for Y=COOEt, CN, and NO 2 in 1, relative to Y=H, as is expected. Large upfield shifts are brought by Y= NMe 2 , OMe, Me, F, Cl, and Br, and downfield shifts by Y= CN and NO 2 in 2, relative to Y=H, with a negligible shift by Y = COOEt. Absolute magnetic shielding tensors of Se (σ(Se)) are calculated for ArSeR (R=H, Me, and Ph), assuming pl and pd, based on the DFT-GIAO method. Observed characters are well explained by the total σ(Se). Paramagnetic terms (σ p (Se)) are governed by (σ p (Se) xx +σ p (Se) yy ), in which the direction of n p (Se) (constructed by 4p z (Se)) is set to the z axis. The main interaction in pl is the n p (Se)-π(C 6 H 4 )-P z (Y) type. The Y dependence in pl occurs through admixtures of 4p z (Se) in π(SeC 6 H 4 Y) and π*-(SeC 6 H 4 Y), modified by the conjugation, with 4p x (Se) and 4p y (Se) in σ-(CSeX) and σ*(CSeX) (X=H or C) under a magnetic field. The main interaction in pd is the σ(CSeX)-π(C 6 H 4 )-p x (Y) type, in which Se-X is nearly on the x axis. The Y dependence in pd mainly arises from admixtures of 4p z (Se) in n p (Se) with 4p,(Se) and 4p y (Se) in modified σ*(CSeX), since n p (Se) is filled with electrons. It is demonstrated that the effect of Y on σ p (Se) in the pl conformation is the same regardless of whether Y is an electron-donor or electron-acceptor, whereas for pd conformations the effect is greater when Y is an electron donor, as observed in 1 and 2, respectively. Contributions of each molecular orbital and each transition on σ p (Se) are evaluated, which enables us to recognize and visualize the effect clearly.

Structures of 1,8-(ArZ)2C14H6O2 and 9-(MeO)-1,8-(ArZ)2C14H7 (Z = S, Se) are determined by X-ray crystallographic analysis. Five C─Z- - -O- - -Z─C atoms of the compounds align linearly, which are analyzed by the extended hypervalent 5c–6e model, based on QC calculations. CT of the 5c–6e occurs as the σ*(C─Z) ← n p (O)→ σ*(Z─C) direction.

The lone pair-lone pair repulsion plays an important role in the nonbonded P·;·;·;P interaction in naphthalene 1,8-positions. The conformations around P and Se in 8-(PhSe)-1-(Ph 2 P=O)C 10 H 6 are determined by the attractive O·;·;·;Se--C 3c-4e type interaction. The P·;·;·;Se interaction in the 1,8-positions is also discussed.

The criteria to distinguish the structure of halogen adducts of aryl chalcogenides in solutions based on the NMR chemical shifts are confirmed by ab initio molecular orbitals (MO) calculations based on the gauge-including atomic orbitals (GIAO) theory. The criteria are applied to determine the structure of halogen adducts of 1,2-bis(phenylselanyl)benzene (1), 1,4-bis(phenylselanyl)benzene (2), and 1,4-bis(p-tert-butylphenylselanyl)benzene (3) (1·nX2, 2·nX2, and 3·nX2, respectively: n=1 and 2 and X=Cl, Br, and I) in CDCl3. The structure of 1·Br2 is demonstrated to be trigonal bipyramidal (TB) not only in the solution but also in crystals. The TB formation of 1·Br2 is just the opposite of the MC (molecular complexes) formation of selenanthrene with bromine in the solution. The driving force for the TB and MC formation is discussed based on the structure of the parent selenides. The structure of 2·2X2 and 3·2X2 is (TB, TB) for X=Cl and Br and (MC, MC) for X=I. On the other hand, the structure of 1·2Br2 is revealed to be TB at one SeBr2 moiety but MC for the other SeBr2 group, which is described as (TB, MC). The bromine exchange is observed in 1·2Br2 in the conditions of NMR measurements. The rate of bromine exchange becomes sharp as excess bromine is added to the 1·2Br2 solution, which shows that the structural (TB, MC)⇄(MC, TB) site exchange in 1·2Br2 is accelerated by the excess bromine and/or its derivatives. Ab initio MO calculations are performed on the adducts to understand their structural features and on the proposed intermediate to confirm the mechanism.

The structure of 1-(methylselanyl)-8-(p-anisylselanyl)naphthalene (2) and 1-(methylselanyl)-8-(p-chlorophenylselanyl)naphthalene (3) was studied by X-ray crystallographic analysis. The structures around the Se−Me and Se−C6H4OMe-p (Se−CAn) groups in 2 are close to type A and type B, respectively: type A if the Se−C bond is almost perpendicular to the naphthyl plane and type B when the Se−C bond is placed on the plane. Those around the Se−Me and Se−C6H4Cl-p (Se−CAr) groups in 3 are type B and type A, respectively. The nonbonded Se···Se distances of 2 and 3 are 3.0951(8) and 3.1239(7) A, respectively. The structure of 3 is very different from that observed in 1-(methylselanyl)-8-(phenylselanyl)naphthalene (1), the structure of which is type C, where the two Se−C bonds decline by about 45° from the naphthyl plane. The structure of 3 strongly suggests the contribution of the nonbonded n(SeAr)···σ*(Se−CMe) three-center−four-electron (3c−4e) type interaction. The nonbonded n(SeMe)···σ*(Se−CAn) 3c−4e type intera...

The 77Se NMR chemical shifts (δobsd(Se)) of p-YC6H4SeMe (1: Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOR (f), and NO2 (g)) and p-YC6H4SePh (2) were determined or redetermined in chloroform-d. The δobsd(Se) values of 2, p-YC6H4SeR (R = CN (3), Bz (4), H (5), Br (6), Et (7), C6H4Y-p (8), CHCH2 (9), CHCHCl-t (10), and CHCH2CCl2-cyclo (11)), 1,1‘-[8-(p-YC6H4Se)C10H6Se]2 (12), and 1-(MeSe)-8-(p-YC6H4Se)C10H6 (13) were plotted against those of 1. The plots were analyzed as two correlations. For example, the points corresponding to a−c make a group (g(m)), and those of d−g belong to another one (g(n)). This must be a reflection of the differences in the dihedral angles between the aryl rings and the Se−R bonds, which should result in the different contributions of the inductive and mesomeric effects of the substituents Y on the δobsd(Se) values. After reexamination of the applicability of the GIAO magnetic shielding tensor for the selenium nucleus (σ(Se)) in selenium compounds of various structures, σ(Se) w...

The X-ray crystallographic analysis of bis[8-(phenylselanyl)naphthyl]-1,1‘-diselenide (1) and 1-(methylselanyl)-8-(phenylselanyl)naphthalene (2) showed that the four selenium atoms in 1 aligned linearly, while the Se−C(Me) and Se−C(Ph) bond in 2 declined by about 50° and 40° from the naphthyl plane, respectively. Ab initio molecular orbital calculations were performed on the models of 1 and 2, model a (HbHc2Se···Ha1Se3SeHa···4SeHbHc) and model b (HaHb1Se···2SeHa‘Hb‘), respectively, with the 6-311++G(3df,2pd) basis sets at the HF and MP2 levels, and the calculations reproduced well the observed structures and revealed the nature of the bonds constructed by the selenium atoms containing nonbonded interactions. The bond with four linearly aligned selenium atoms in model a can be analyzed with the 4c-6e model constructed with the nonbonded interaction between the two p-type lone pairs on the outside selenium atoms and the σ*(Se−Se) orbital of the inside Se−Se bond, which results in charge transfer from the ou...

The X-ray crystallographic analysis of 8-fluoro-1-(p-anisylselanyl)naphthalene (1) revealed that the F and Se atoms and the ipso-carbon of the p-anisyl group (C(An)) aligned linearly. The F atom and the Se−C(An) bond lay on the naphthyl plane: the nonbonded distance between F and Se atoms was 2.753(3) A and the FSeC(An) angle was 175.0(1)°. Ab initio MO calculations with the 6-311++G(3df,2pd) basis sets performed on the model compound of 1, HF···SeH2, where the aryl groups of 1 were replaced by hydrogens. The calculations exhibited that the energy minimum was achieved when the F, Se, and C(An) atoms aligned linearly. Charge transfer in the formation of HF···SeH2 was suggested to occur from F to SeH2 on the basis of natural population analysis, which supported the npx(F)−σ*(Se−C(An)) interaction.

Role of dG(b)(r(c))/dw and dV(b)(r(c))/dw is revealed as the basic atoms-in-molecules (AIM) functions to evaluate, classify, and understand the nature of interactions, as well as G(b)(r(c)) and V(b)(r(c)). The border area between van der Waals (vdW) adducts and hydrogen-bonded (HB) adducts is shown to appear at around dG(b)(r(c))/dw = -dV(b)(r(c))/dw and that between molecular complexes (MC) and trigonal bipyramidal adducts (TBP) of chalcogenide dihalides appears at around 2dG(b)(r(c))/dw = -dV(b)(r(c))/dw. H(b)(r(c)) are plotted versus H(b)(r(c)) - V(b)(r(c))/2 at bond critical points (BCPs) in the AIM dual functional analysis. The plots incorporate the classification of interactions by the signs of ∇(2)ρ(b)(r(c)) and H(b)(r(c)). R [= (x(2) + y(2))(1/2)] corresponds to the energy for the interaction in question at BCPs, where (x, y) = (H(b)(r(c)), H(b)(r(c)) - V(b)(r(c))/2) and (x, y) = (0, 0) at the origin. The segment of lines for the plots (S) should correspond to energy, if the segment is substantially linear. The first derivative of S (dS) is demonstrated to be proportional to R. Relations between AIM functions, such as dV(b)(r(c))/dw, dG(b)(r(c))/dw, dH(b)(r(c))/d[H(b)(r(c)) - V(b)(r(c))/2], d(2)V(b)(r(c))/dw(2), d(2)G(b)(r(c))/dw(2), and d(2)H(b)(r(c))/d[H(b)(r(c)) - V(b)(r(c))/2](2), are also discussed. The results help us to understand the nature of interactions.

(n)J(Se,Se) (n=1-4) nuclear couplings between Se atoms were analyzed by using molecular orbital (MO) theory as the first step to investigating the nature of bonded and nonbonded (n)J(Se,Se) interactions between Se atoms. The values were calculated by employing Slater-type triple xi basis sets at the DFT level, which were applied to structures optimized with the Gaussian 03 program. The contribution from each occupied MO (psi(i)) and psi(i)--psi(a) (psi(a)=unoccupied MO) transition was evaluated separately. 1J(Se,Se) was calculated for the MeSeSeMe model compound, which showed a typical dependence on the torsion angle (phi(C(Me)SeSeC(Me))). This dependence explains the small values (or =64 Hz) of 1Jobsd(Se,Se) observed for RSeSeR' and large values (330-380 Hz) of 1Jobsd(Se,Se) observed for 4-substituted naphtho[1,8-c,d]-1,2-diselenoles, which correspond to synperiplanar diselenides. The HOMO--LUMO and HOMO-1--LUMO transitions contribute the most to 1J(Se,Se) at phi=0 and 180 degrees to give large values of 1J(Se,Se), whereas various transitions contribute and cancel each other out at phi=90 degrees to give small values of 1J(Se,Se). Large 4Jobsd(Se,Se) values were also observed in the nonbonded Se...Se, Se...Se=O, and O=Se...Se=O interactions at naphthalene 1,8-positions. The Fermi contact (FC) term contributes significantly to 4J(Se,Se), whereas the paramagnetic spin-orbit (PSO) term contributes significantly to 1J(Se,Se). 2J(Se,Se) and 3J(Se,Se) were analyzed in a similar manner and a torsional angular dependence was confirmed for 3J(Se,Se). Depending on the structure, the main contribution to (n)J(Se,Se) (n=2, 3) is from the FC term, with a lesser contribution from the PSO term. Analysis of each transition enabled us to identify and clearly visualize the origin and mechanism of the couplings.

The orientational effect ofp-YC6H4(Ar) onδ(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. Sets ofδ(Se) are proposed forplandpdemploying 9-(arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquinones (2), respectively, where Se–CRin ArSeR is on the Ar plane inpland perpendicular to the plane inpd. Absolute magnetic shielding tensors of Se (σ(Se)) are calculated for ArSeR (R = H, Me, and Ph), assumingplandpd, with the DFT-GIAO method. Observed characters are well reproduced by the total shielding tensors (σt(Se)). The paramagnetic terms (σP(Se)) are governed byσP(Se)xx+σP(Se)yy, where the direction ofnP(Se) is set to thez-axis. The mechanisms of the orientational effect are established both forplandpd. Sets ofδ(Se:1) andδ(Se:2) act as the standards forplandpd, respectively, whenδ(Se) of ArSeR are analyzed based on the orientational effect.

delta((8)Se) values for 1-[8-(p-YC(6)H(4)Se)C(10)H(6)]SeSe[C(10)H(6)(SeC(6)H(4)Y-p)-8']-1' (1: Y = H, OMe, Me, Cl, Br, COOEt, and NO(2)) showed a good correlation with those of 1-(MeSe)-8-(p-YC(6)H(4)Se)C(10)H(6) (2). While the delta((1)Se) values correlated well with delta((8)Se) in 2 with a positive proportionality constant of 0.252 (regular correlation), a similar correlation for 1 gave a negative proportionality constant of -0.282 (inverse correlation). To clarify the mechanism associated with the inverse correlation in 1, together with the regular correlation in 2, ab initio MO calculations, containing the GIAO magnetic shielding tensor for the Se nucleus (sigma(Se)), were performed on p-YC(6)H(4)(A)SeH- - -(B)SeH-(B)SeH- - -H(A)SeC(6)H(4)Y-p (3: model of Se(4) 4c-6e for 1) and on p-YC(6)H(4)(A)SeH- - -(B)SeH(2) (4 and 5: models of Se(2) pi type 2c-4e and (A)Se- - -(B)Se-H 3c-4e for 2, respectively) with the 6-311+G(2d,p) basis sets at B3LYP and/or HF levels. The characteristic nature of the substituent effects on atomic charges and delta(Se) values in 3 is demonstrated to be Y(delta-)--C(6)H(4)-Se(delta)(+)- - -Se(delta)(+)-Se(delta)(+)- - -Se(delta)(+)-C(6)H(4)--Y(delta-) and Y(delta-)--C(6)H(4)-Se(down)- - -Se(up)-Se(up)- - -Se(down)-C(6)H(4)--Y(delta-), respectively, (Y = electron-withdrawing) and in 5 is Y(delta-)--C(6)H(4)-Se(delta)(+)- - -Se(delta)(-)-H(delta)(+) and Y(delta-)--C(6)H(4)-Se(down)- - -Se(down)-H(down), respectively. In the case of 4, a substantial contribution through the naphthylidene group is suggested. These results indicate that the nature of the interaction between the linear four Se atoms in 1 is of the 4c-6e type and that between the two Se atoms in 2 is pi type 2c-4e and/or 3c-4e according to the conformations around the Se atoms. The observed NMR parameters are well explained by model calculations on 3-5. Plots of (4)J((1)Se,(8)Se) versus delta((8)Se) of 1 and 2 gave good correlations with negative proportionality constants, which indicates that the J values become larger as the electron density on the (8)Se atoms increases.

Secondary imidazole-appended beta-cyclodextrin 5 with a nondistorted cavity synthesized from a novel intermediate 3-amino-3-deoxy-beta-cyclodextrin exhibits much greater catalytic activity in the ester hydrolysis than its isomer 6 with a distorted cavity, indicating that the catalytic activities of secondary functional cyclodextrins are dependent on cavity structures.

Magnitudes of the p(Z)-π(Ar/Nap) conjugation were evaluated for 1-(arylchalcogena)naphthalenes (1-(ArZ)Nap, 1-(p-YC(6)H(4)Z)C(10)H(7); 1 (Z = Te), 2 (Se), 3 (S) and 4 (O)). Structures of 1 were determined by X-ray analysis for Y = NMe(2) (b), OMe (c) and CN (i). For 1b and 1c that have electron donating Y, the Z-C(Ar) bond is located on the naphthyl plane with Z-C(Nap) being perpendicular to the aryl plane, which we define as (B: pd). On the other hand, the structure of 1i with electron donating Y is (A: pl), of which Z-C(Ar) is placed almost perpendicular to the naphthyl plane with Z-C(Nap) being located on the aryl plane. Each structure of 1a (Y = H), 1b, 1c, 1d (Me), 1e (F), 1f (Cl), 1g (Br), 1h (COOEt), 1i and 1j (NO(2)) was determined by NMR in chloroform-d. Structures of 1 in the solutions are (B: pd) for b, c and e that have electron donating Y, (A: pl) for f-j with electron accepting Y, and in equilibrium between (B: pd) and (A: pl) for a and d of which Y are rather neutral. The results for 2-4 are very similar to those of 1 in solutions. Quantum chemical calculations were performed on 1-4 with Y of a, b' (NH(2)), d, f and j. Magnitudes of the p(Z)-π(Ar/Nap) conjugation were well-evaluated by NBO (natural bond orbital) analysis. The values were 12.6 and 13.0 kcal mol(-1) for the typical forms of (A: pl) and (B: pd) of 1a, respectively, resulting in a much smaller energy difference between the two (0.4 kcal mol(-1)), which should correspond to the observed result. It is well-demonstrated that the p(Te)-π(Ar/Nap) conjugation operates effectively in 1, although the magnitudes increase in the order of Z = TeSeSO. Thermal effect of the Gibbs free energies is shown to play an important role in the energy profiles of 1a-4a.

The four sulfur atoms in bis[8-(phenylthio)naphthyl]-1,1'-disulfide are demonstrated to align linearly by the X-ray crystallographic analysis, where the linear S4 alignment is stabilized by the four-centre six-electron interaction.

A series of selenium and tellurium bis(carbodithioates and carbothioates) were synthesized. X-Ray structure analysis revealed that Se(SSCC(6)H(4)OMe-2)(2), Te(SSCC(6)H(4)OMe-2)(2) and Te(SSCC(6)H(4)Me-4)(2) have trapezoidal-planar configuration of ES(4) (E = Se, Te) and despite the larger atomic radii, the C=S···Te distances in Te(SSCC(6)H(4)OMe-2)(2) are comparable to those in the corresponding selenium derivatives Se(SSCC(6)H(4)OMe-2)(2). Molecular-orbital calculations performed on compounds E(E'SCR)(2) (E = S, Se, Te; E' = O, S; R = Me, Ph, C(6)H(4)OMe-2) showed that the syn-conformers of Se(SSCR)(2) and Te(SSCR)(2) are more stable than the corresponding anti-ones, while, in the case of carbothioic acid derivatives, E(SOCR)(2) showed that their anti-conformers are all more stable than the corresponding syn-ones. Natural bond orbital (NBO) analyses of these dithio-compounds revealed that two types of orbital interactions, n(S(1))→σ*(E-S(2)) and n(O)→σ*(E-S(2)), play a role in the bonding of E[S(2)S(1)CC(6)H(4)OMe-2](2) (E = Se, Te) and the former play a particularly predominant role.