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

We report the structural dependency of long range scalar J-coupling constant across four bonds as function of the dihedral angles phi 1 and phi 3. 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 degrees for both phi 1 and phi 3, 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.