Elucidating heteroatom influence on homonuclear 4J(H,H) coupling constants by DFT/NMR approach |
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Authors: | Maria Giovanna Chini Daniele Urbani Paolo Dambruoso Raffaele Riccio Giuseppe Bifulco |
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Affiliation: | 1. Department of Pharmacy, University of Salerno, Fisciano, Italy;2. Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Bologna, Italy |
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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 4J(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 4J(H,H) calculated values, tabulated for variation of 30° for both Φ1 and Φ3, have disclosed an unexpected detectable coupling constant (4J(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 4J(H,H) values obtained at density functional theory for the system 4 have reproduced with good accuracy an unexpected experimental 4J(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. |
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Keywords: | 1H conformational analysis density function theory nuclear magnetic resonance heteroatoms long-range coupling constant organic synthesis |
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