In a previous study, we published five crystal structures of the eight possible isomers of methyl 3,&nhydrohexofuranosides1. Of special interest was how the anomeric effect* could dominate the shape and pucker of otherwise highly flexible furanoid rings in these compounds. In accordance with previous 'H-n.m.r. investigations in solution j, the results showed that the conformations of the furanoid rings correspond to an almost quasi-axial orientation of the aglycon and that the driving force is the abovementioned stereoelectronic effect. In all cases, the-influence of the exo-anomeric effect was also observed'.
Since the quality of the crystals of a sixth isomer, namely, the title compound 1, was relatively poor, it was at first not possible to determine the crystal structure of this compound. Late+, with the help of the computer programme SHELXS-845, the phase problem was solved by using direct methods and the least-squares method for refinementl. We now report the results of this structure determination.
Methyl 3,6-anhydr+L-gulofuranoside3 (1) crystakes in the monoclinic space group P2, with two independent molecules in the asymmetric unit. Furrher crystallographic information is given in Table I.
The final positional and thermal parameters are listed in Table II. Bond lengths and bond angles are given in Tables III andIV. A SCHAKAL representation' of one of the independent molecules (I) is shown in Fig. 1, from which also the atom numbering scheme can be deduced*. *Lists of observed and calculated struchue amplitudes, atomic coordinaka of the hydrogen atoms (calculated), and to&m auglea are deqxmited with, and cm be obtained from, Elaevier Science Publishers B.V., BBA Data Dcpoaition, P.O. Box 1527, Ameterdam, The Netherlandr. Rekracc should be made to No. BBA/DD/374/Carbo/tyt.ir. Ret., 168 (1987) 115-119.