Torsional Angular Dependence of 1J(Se,Se) and Fermi Contact Control of 4J(Se,Se): Analysis of nJ(Se,Se) (n=1–4) Based on Molecular Orbital Theory

✍ Scribed by Waro Nakanishi; Satoko Hayashi

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 754 KB
• Volume: 14
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200701532

✦ Synopsis

Abstract

^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 ξ basis sets at the DFT level, which were applied to structures optimized with the Gaussian 03 program. The contribution from each occupied MO (ψ~i~) and ψ~i~→ψ~a~ (ψ~a~=unoccupied MO) transition was evaluated separately. ^1^J(Se,Se) was calculated for the MeSeSeMe model compound, which showed a typical dependence on the torsion angle (ϕ(C~Me~SeSeC~Me~)). This dependence explains the small values (≤64 Hz) of ^1^J~obsd~(Se,Se) observed for RSeSeR′ and large values (330–380 Hz) of ^1^J~obsd~(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 ^1^J(Se,Se) at ϕ=0 and 180° to give large values of ^1^J(Se,Se), whereas various transitions contribute and cancel each other out at ϕ=90° to give small values of ^1^J(Se,Se). Large ^4^J~obsd~(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 ^4^J(Se,Se), whereas the paramagnetic spin‐orbit (PSO) term contributes significantly to ^1^J(Se,Se). ^2^J(Se,Se) and ^3^J(Se,Se) were analyzed in a similar manner and a torsional angular dependence was confirmed for ^3^J(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.