Elucidating heteroatom influence on homonuclear 4 J(H,H) coupling constants by DFT/NMR approach.

Abstract

We report the structural dependency of long range scalar J-coupling constant across four bonds as function of the dihedral angles Φ1 and Φ3. The calculated homonuclear coupling constants 4 J(H,H ), obtained at a density functional theory level, were measured between C(1)─X(2) and X(2)─C(3) bonds in three-term models, where C, N, O, and S were systematically used as the second atom of the alkyl structures (1-4). The 4 J(H,H) calculated values, tabulated for variation of 30° for both Φ1 and Φ3, have disclosed an unexpected detectable coupling constant (4 J(H,H ) ≥ 1 Hz) across heteroatoms, useful to provide valuable structural information. A 2-methyl-1,3-dithiane sulfide (5) was used as a case study to prove the applicability and reliability of the calculated values to real issues. The 4 J(H,H ) values obtained at density functional theory for the system 4 have reproduced with good accuracy an unexpected experimental 4 J(H2ax-H4ax ) = 1.01 Hz of sulfide molecule (5), suggesting these calculated coupling constant values as a new powerful tool for the organic synthesis and stereochemical analysis.