N-{4-[(3,4-Dimethylphenyl)(ethyl)sulfamoyl]phenyl}-N-ethylacetamide

When viewed down the central S⋯N axis of the title compound, C20H26N2O3S, it is apparent that the molecule adopts a gauche conformation with all O atoms lying to one side of the central benzene ring; the carbonyl O atom is directed away from the central ring and the N-bound ethyl groups lie to one side of the molecule. Supramolecular helical chains aligned along the b axis and sustained by C—H⋯O contacts feature in the crystal packing. These are consolidated in the three-dimensional structure by C—H⋯π interactions.

When viewed down the central SÁ Á ÁN axis of the title compound, C 20 H 26 N 2 O 3 S, it is apparent that the molecule adopts a gauche conformation with all O atoms lying to one side of the central benzene ring; the carbonyl O atom is directed away from the central ring and the N-bound ethyl groups lie to one side of the molecule. Supramolecular helical chains aligned along the b axis and sustained by C-HÁ Á ÁO contacts feature in the crystal packing. These are consolidated in the three-dimensional structure by C-HÁ Á Á interactions.
Cg1 is the centroid of the C3-C8 ring.
With reference to the central benzene ring in (I), Fig. 1, the S1 [deviation = -0.068 (1) Å] and N2 [-0.005 (1) Å] atoms are co-planar. Both sulfonamide-O atoms lie to the same side of the plane as does the carbonyl-O atom, which is directed away from the ring, with the remaining substituents lying to the other side. When viewed down the S1···N2 vector, both N-bound ethyl groups lie to the same side of the molecule. Similarly, when viewed down the S1···N2 vector, the molecule has a gauche conformation.
In the crystal packing, molecules are connected into a helical supramolecular chain along the b axis via C-H···O contacts occurring between benzene-H and sulfonamide-O atoms, Table 1 and Fig. 2. The chains are consolidated in the crystal packing by C-H···π interactions, Table 1 and Fig. 3.

Experimental
A mixture of N-{4- [(3,4-dimethylphenyl)sulfamoyl]phenyl}acetamide 100 mg (0.314 mmol) and sodium hydride 85 mg (0.78 mmol) in N,N-dimethylformamide (10 ml) was stirred at room temperature for 30 min. followed by addition of ethyl iodide 199 µl (0.785 mmol). Stirring was continued for a further 3 h and the contents were poured over crushed ice. The precipitate that formed was isolated, washed and crystallized from methanol solution by slow evaporation; M.pt. 472 K.
In the final refinement four low angle reflections evidently effected by the beam stop were omitted, i.e. (100), (002), (011) and (111). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 35% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.