Hexopyranose resonance spectroscopy

Most aldohexopyranoses exist in a chair form in which the hydroxymethyl group at C(5) assumes an equatorial position. All the P-D-hexopyranoses exist predominantly in the 4Ci form since the alternative C4 conformer involves a large unfavourable xyn-diaxial interaction between the hydroxymethyl and anomeric group (Figure 1.8). Most of the a-D-hexopyranosides also adopt the 4Ci conformation preferentially. Only ot-idopyranoside and a-D-altropyranose show a tendency to exist in the C4 conformation, and they coexist with the alternative 4Ci conformations according to H-NMR (hydrogen nuclear magnetic resonance) spectroscopy studies. 

Recently, all eight diastereoisomeric 1,6-anhydro-P-D-hexopyranoses and three related model compounds have been studied in O-depleted water using 1 0 NMR spectroscopy methodology [94,97]. Chemical shift assignments for all resonances in the eleven compounds were made. The results for glucosan ( 95), mannosan( 96), and galactosan ( 97) as well as the three model compounds 98-100 are shown below. 

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