The title compound, C18H12Cl2N2OS, consists of a dihydrobenzothiazine unit linked by a –CH group to a 2,4-dichlorophenyl substituent, and to a propanenitrile unit is folded along the S...N axis and adopts a flattened-boat conformation. The propanenitrile moiety is nearly perpendicular to the mean plane of the dihydrobenzothiazine unit. In the crystal, C—HBnz...NPrpnit and C—HPrpnit...OThz (Bnz = benzene, Prpnit = propanenitrile and Thz = thiazine) hydrogen bonds link the molecules into inversion dimers, enclosing R 2 2(16) and R 2 2(12) ring motifs, which are linked into stepped ribbons extending along [110]. The ribbons are linked in pairs by complementary C=O...Cl interactions. π–π contacts between the benzene and phenyl rings, [centroid–centroid distance = 3.974 (1) Å] may further stabilize the structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (23.4%), H...Cl/Cl...H (19.5%), H...C/C...H (13.5%), H...N/N...H (13.3%), C...C (10.4%) and H...O/O...H (5.1%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. Computational chemistry calculations indicate that the two independent C—HBnz...NPrpnit and C—HPrpnit...OThz hydrogen bonds in the crystal impart about the same energy (ca 43 kJ mol−1). Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

The title compound, C18H12FNOS, is built up from a 4-fluorobenzylidene moiety and a dihydrobenzothiazine unit with a propynyl substituent, with the heterocyclic portion of the dihydrobenzothiazine unit adopting a shallow boat conformation with the propynyl substituent nearly perpendicular to it. The two benzene rings are oriented at a dihedral angle of 43.02 (6)°. In the crystal, C—HFlurphen...FFlurphen (Flurphen = fluorophenyl) hydrogen bonds link the molecules into inversion dimers, enclosing R 2 2(8) ring motifs, with the dimers forming oblique stacks along the a-axis direction. Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H...H (33.9%), H...C/C...H (26.7%), H...F/F...H (10.9%) and C...C (10.6%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

The conformation of the 2-ethoxy-2-oxoethoxy side chain, including a gauche Ce—O—C—C3 [72.46 (16)°] (e = ethoxy) unit, in the title compound, C18H19NO7, is partly determined by an intramolecular C—H...O hydrogen bond. In the crystal, C—H...O hydrogen bonds and C—H...π interactions arising from the same methylene group form chains extending along the a-axis direction.

The title compound, C20H16Cl2N2O3S, is built up from a dihydrobenzothiazine moiety linked by –CH– and –C2H4– units to 2,4-dichlorophenyl and 2-oxo-1,3-oxazolidine substituents, where the oxazole ring and the heterocyclic portion of the dihydrobenzothiazine unit adopt envelope and flattened-boat conformations, respectively. The 2-carbon link to the oxazole ring is nearly perpendicular to the mean plane of the dihydrobenzothiazine unit. In the crystal, the molecules form stacks extending along the normal to (104) with the aromatic rings from neighbouring stacks intercalating to form an overall layer structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (28.4%), H...Cl/Cl...H (19.3%), H...O/O...H (17.0%), H...C/C...H (14.5%) and C...C (8.2%) interactions. Weak hydrogen-bonding and van der Waals interactions are the dominant interactions in the crystal packing. Density functional theory (DFT) optimized structures at the B3LYP/ 6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO—LUMO behaviour was elucidated to determine the energy gap.

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