The twinning of two closely related phenylisoxazoles interpreted according to order-disorder theory

Abstract

Abstract The closely related 5-[(1Z)-2-(methylthio)-1-propen-1-yl]-3-(4-nitrophenyl)isoxazole (I) and 3-(4-methoxyphenyl)-5-[(1Z)-2-(methylthio)-1-propen-1-yl]isoxazole (II) were synthesized by consecutive ring fragmentation and cycloaddition and their crystal structures were determined by X-ray single crystal diffraction at 100 K. Both compounds are twinned by mirroring at (100). The nitrophenyl (I) [P21/c, Z = 8, Z′ = 2, a = 32.1827(10) Å, b = 5.5992(2) Å, c = 13.9145(4) Å, β = 102.2428(14)°, R obs = 0.048, 6408 F data, 344 parameters] crystallizes as an order-disorder (OD) structure of one kind of layers. The twin individuals are polytypes of a maximum degree of order (MDO). The twin boundary is interpreted as a triple of adjacent layers of the second MDO polytype. The methoxyphenyl (II) [P21/c, Z = 4, Z′ = 1, a = 16.0545(7) Å, b = 5.6575(3) Å, c = 13.8891(7) Å, β = 94.334(3)°, R obs = 0.039, 3365 F data, 164 parameters] can be described as an OD structure composed of two kinds of layers, made up of —CH2—-fragments of the S-methyl groups and the remaining parts of the (II) molecules, respectively. Of the four MDO polytypes, one corresponds to the twin individuals. The twin boundary is composed of layer triples of either of two other MDO polytypes.