Methyl 6-azido-6-deoxy-α-d-galactoside

The structure of the title compound, C7H13N3O5, was solved using data from a multiple fragment crystal. The galactoside ring adopts a 4 C 1 chair conformation. In the crystal, the molecules are linked by strong O—H⋯O hydrogen bonds, which build linkages around the screw axis of the cell in a similar way to the iodo analogue. These C-5 and C-6 packing motifs expand to R 2 2(10), C 2 2(7) and C 2 2 2(8) motifs, as found in closely related compounds.

The structure of the title compound, C 7 H 13 N 3 O 5 , was solved using data from a multiple fragment crystal. The galactoside ring adopts a 4 C 1 chair conformation. In the crystal, the molecules are linked by strong O-HÁ Á ÁO hydrogen bonds, which build linkages around the screw axis of the cell in a similar way to the iodo analogue. These C-5 and C-6 packing motifs expand to R 2 2 (10), C 2 2 (7) and C 2 2 2 (8) motifs, as found in closely related compounds.
Close similarity with the iodo analogue is observed: the major difference concerns the approximately doubled c axis length and the presence of the two additional 2 1 screw axes in the latter orthorhombic crystal.

Refinement
The crystals were predominantly multiple-fragment blocks up to ~0.7 x 0.6 x 0.2 mm in size. The minute crystal which was finally selected consisted of one major fragment with some minor fragments along the long (needle) axis. In addition, the data collection was partially marred by crystal movement initiated by ice buildup. The dataset arises from processing the remaining 155 screens of data after removing the affected 66 slices which were identified by the screen review statistics; this was verified by visual inspection of the screens which showed misalignment and ice rings. In the (automatic) processing, a further 209 outliers were detected and removed. High angle data was also recognized as being weak or suffering from misalignent, so the data outside the 0.92 Å shell was omitted using the SHEL command. A further 20 outlier reflections (ΔF 2 /σ(F 2 )>4.2) were removed from the refinement; some of these could be identified as being affected by ice-diffracted scattering or behind the goniometer shadow. As a result, the final dataset is significantly less than 100% complete but is adequate for defining the structure; defining the absolute configuration, known from the synthetic procedure, is not possible.
supplementary materials sup-2 The hydroxyl atom HO4 on oxygen O4 was not placed correctly using the usual SHELX (AFIX 147) command, as determined by packing analysis inspection. It was placed, and then freely refined, on the basis of careful difference mapping around the O4 site and restrained to be 0.84 (3) Å from O4 using DFIX. The other hydroxyl H atoms were refined by automatic placement at positions indicated by a difference electron density map and their positions were constrained to refine on their parent O atoms with O-H 0.84 Å (using AFIX 147). The hydroxyl H atoms were refined with U iso (H) = 1.5U eq (O).
The methyl H atoms were constrained to an ideal geometry (C-H = 0.98 Å) with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the adjacent C-C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances of 1.00 (primary) or 0.99 (methylene) Å and and with U iso (H) = 1.2U eq (C). Fig. 1. Asymmetric unit contents of (I) (Farrugia, 1997) at the 30% thermal ellipsoid level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.