Sucralose, a trichlorinated derivative of sucrose (4,1',6'-trichloro-4,1',6'-trideoxy-galacto-sucrose), is approximately 650 times sweeter than sugar on a mass basis. It has a sucrose-like taste profile, with no unpleasant aftertaste, while being noncaloric and noncariogenic. This sweetener is emerging as the most commercially useful compound in the field of sucrochemistry. The conformational behavior of aqueous sucralose was studied by NMR and computerized molecular modeling. Steady-state NOEs at 400.13 MHz and transient NOEs at both 250.13 and 400.13 MHz have been measured. Long-range C-13-H-1 coupling constants are also reported. In parallel, the complete conformational analysis of the disaccharide has been achieved with two different molecular mechanics methods. The conformation of the pyranose ring is confirmed by the excellent agreement between the experimental and theoretical intracyclic scalar coupling constants. The furanoid ring is shown to exhibit some flexibility, covering the four adjacent 3E, 4T3, 4E, and 4T5 shapes. Within the potential energy surfaces calculated for the disaccharide, four families of stable conformers can be identified. One of these corresponds closely to the crystalline conformation of sucralose not only in terms of conformation about the glycosidic linkage but also in terms of orientation of the chloromethyl groups and occurrence of the interresidue hydrogen bond. The 3J(C-H) coupling constant about the glycosidic linkage was calculated using an equation suitable for COCH segments. The data do not support a single conformational model, and only conformational averaging can provide agreement between theoretical and experimental parameters. The theoretical NMR relaxation data were calculated taking into account all the accessible conformations and using the averaging methods appropriate for both slow and fast internal motions. In agreement with a recent solution dynamics simulation of beta-maltose, the relaxation data suggest that the large-amplitude interglycosidic torsional motions of sucralose are occurring on a time scale similar to that of molecular reorientation. This extensive molecular-modeling investigation provides a good description of the conformational behavior of both aqueous and crystalline sucralose.