All couplings related to the
O5-C5-C6-O6 (ω) torsion in hexopyranoses can be calculated
as decribed by Stenutz
et al.. θ is the C5-C6-O6-O6H torsion and it is required for
the calculation of 1J and 2J values.
A value for θ is required for most coupling calculations. In most cases a value of 60° will give reasonable results since gauche dominates in most derivatives. Notable exceptions are compounds with large substituents at O6, such as glycosyl residues (6-linked disaccharides) or trityl groups.
"Hydroxymethyl Group Conformation in Saccharides: Structural Dependence of 2JHH, 3JHH,and 1JCH Spin-Spin Coupling Constants"
R. Stenutz, I. Carmichael, G. Widmalm & A.S. Serianni; J. Org. Chem. 67 (2002) 949-958.
"Correlated C-C and C-O bond conformations in saccharide hydroxymethyl groups: parametrization and application of redundant 1H-1H, 13C-1H, and 13C-1C NMR J-couplings"
C. Thibaudeau, R. Stenutz, B. Hertz, T. Klepach, S. Zhao, Q. Wu, I. Carmichael & A.S. Serianni; J. Am. Chem. Soc. 126 (2004) 15668-15685.