Hydroxymethyl Group Conformation in Saccharides: Structural Dependencies of 2JHH, 3JHH, and 1JCH Spin−Spin Coupling Constants
- 11 January 2002
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 67 (3) , 949-958
- https://doi.org/10.1021/jo010985i
Abstract
Experimental and theoretical methods have been used to correlate 2JHH and 3JHH values within the exocyclic hydroxymethyl groups (CH2OH) of saccharides with specific molecular parameters, and new equations are proposed to assist in the structural interpretation of these couplings. 3JHH depends mainly on the C−C torsion angle (ω) as expected, and new Karplus equations derived from J-couplings computed from density functional theory (DFT) in a model aldopyranosyl ring are in excellent agreement with experimental values and with couplings predicted from a previously reported general Karplus equation. These results confirm the reliability of DFT-calculated 1H−1H couplings in saccharides. 2JHH values depend on both the C−C (ω) and C−O (θ) torsions. Knowledge of the former, which may be derived from other parameters (e.g., 3JHH), allows θ to be evaluated indirectly from 2JHH. This latter approach complements more direct determinations of θ from 3JHCOH and potentially extends these more conventional analyses to O-substituted systems lacking the hydroxyl proton. 1JCH values within hydroxymethyl fragments were also examined and found to depend on rCH, which is modulated by specific bond orientation and stereoelectronic factors. These latter factors could be largely, but not completely, accounted for by C−C and C−O torsional variables, leading to only semiquantitative treatments of these couplings (details discussed in the Supporting Information). New equations pertaining to 2JHH and 3JHH have been applied to the analysis of hydroxymethyl group J-couplings in several mono- and oligosaccharides, yielding information on C5−C6 and/or C6−O6 rotamer populations.Keywords
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