The title compound, 0.759C19H21ClN2O2S·0.241C19H21ClN2O2S, was synthesized by aryl­sulfonyl­ation of 2-n-butyl-5-chloro-1H-benzimidazole in the presence of triethyl­amine. The crystal structure is composed of two mol­ecules, 2-n-butyl-6-chloro-1-(2,4-dimethylphenyl­sulfon­yl)-1H-benzimidazole and 1-(2,4-dimethylphenyl­sulfon­yl)-2-n-butyl-5-chloro-1H-benz­imidazole, in the refined ratio of 0.759 (4):0.241 (4) disordered at the same position in the unit cell. The mol­ecule has three essentially planar fragments viz. benzimidazole, dimethyl­benzene and n-butyl (r.m.s. deviations of 0.009, 0.024 and 0.003 Å, respectively). The angle between the benzimidazole and dimethyl­benzene fragments is 86.0 (1)°. In the crystal, pairs of inter­molecular C—H⋯π inter­actions form centrosymmetrical dimers, which are linked by weak inter­molecular C—H⋯O hydrogen bonds.

By arylsulfonylation of cytisine in the presence of triethylamine, three new compounds have been obtained in good yields: (7R,9R)-N-[(4-ethylphenyl)sulfonyl]cytisine, C19H22N2O3S (I) {systematic name: (1R,5R)-3-[(4-ethylphenyl)sulfonyl]-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocin-8-one}, (7R,9R)-N-[(4-chlorophenyl)sulfonyl]cytisine, C17H17ClN2O3S (II) {systematic name: (1R,5R)-3-[(4-chlorophenyl)sulfonyl]-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocin-8-one} and (7R,9R)-N-[(3-nitrophenyl)sulfonyl]cytisine, C17H17N3O5S (III) {systematic name: (1R,5R)-3-[(3-nitrophenyl)sulfonyl]-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocin-8-one}. The crystal structures of the compounds were determined on the basis of single-crystal X-ray diffraction data. The crystal structures of (I)–(III) are distinguished by the arrangement of two fragments of the molecule around the sulfonyl site. For all structures, weak C—H...O hydrogen bonds are developed. Hirshfeld surface analysis shows that H...H (for I and II) and H...O/O...H (for III) interactions make the most important contribution to the crystal packing.

The title compound, C17H18N2O2S, was synthesized by aryl­sulfonyl­ation of 1-hy­droxy­methyl-1H-benzimidazole in the presence of triethyl­amine. The benzimidazole and benzene rings form a dihedral angle of 84.1 (1)°. The tert-butyl group was treated as rotationally disordered over two orientations in a 0.51 (2):0.49 (2) ratio. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into chains propagating in [010].

Mixed crystals of 1-(4-chlorophenylsulfonyl)-2,5-dimethyl-1H-benzimidazole and 1-(4-chlorophenylsulfonyl)-2,6-dimethyl-1H-benzimidazole (ratio 0.707:0.293; two molecules in the asymmetric unit), 0.707C15H13ClN2O2S·0.293C15H13ClN2O2S, (I), and of 2-n-butyl-1-(4-tert-butylphenylsulfonyl)-5-chloro-1H-benzimidazole and 2-n-butyl-1-(4-tert-butylphenylsulfonyl)-6-chloro-1H-benzimidazole [ratio 0.731 (2):0.269 (2); one molecule in the asymmetric unit], 0.731C21H25ClN2O2S·0.269C21H25ClN2O2S, (II), were obtained from the arylsulfonylation reaction of the corresponding 2-alkylbenzimidazoles. In addition, two products were obtained from the reaction of 2-n-butyl-5-chloro-1H-benzimidazole with 4-methylbenzenesulfonyl chloride. These reaction products were separated by column chromatography and the crystal structure of one of the products, 2-n-butyl-5-chloro-1-(4-methylphenylsulfonyl)-1H-benzimidazole (one molecule in the asymmetric unit), C18H19ClN2O2S, (III), was determined. In the crystal structures of (I)–(III), there is a difference in the arrangement of the planar benzimidazole and arylsulfonyl fragments. The formation of weak C—H...O hydrogen-bonding interactions is characteristic of all three crystal structures.

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