
TY  - JOUR
A1  - Becker, H 
A1  - Raston, CL 
A1  - Skelton, BW 
A1  - White, AH 
T1  - Substituent Effects in the Crystal Structures of Isoxindigos [(<i>E</i>)-3,3'-Bibenzofuranylidene-2,2'-diones]
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1985
VL  - 38
IS  - 1
SP  - 85
EP  - 96
KW  - 
UR  - https://doi.org/10.1071/CH9850085 
N2  - Single-crystal X-ray structure determinations of the parent isoxindigo (1), C16H8O4, together with those of derivatives substituted in both benzene rings with ( i ) t-butyl groups in the 5- and 7-positions [derivative (2)] and (ii) methoxy and t-butyl groups in the 5- and 7- positions respectively [two polymorphs, (3&#945;,8)] have been determined in order to examine the possibility of distortion of molecular planarity by substituent  steric effects, and the spectroscopic consequences thereof. Crystals of (1) are monoclinic, P21/n, a 17.69(1), b 5.690(3), c5.693(3)&#506;, &#946; 100.52(5)°, Z 2; after least-squares refinement, a residual R 0.067 was obtained for No 385 ?observed? Independent reflections. For (2), C32H40O4, crystals are monoclinic, P21/n, a 16.402(8), b 12.313(6), c 13.913(8)&#506;, &#946; 96.75(4)°, Z4; R 0.088 for No 1261. For (3), C26H28O6 (&#945;-form), crystals are orthorhombic, Pcab , a 10.449(4), b 12.477(4), c 17.825(6)&#506;, Z 4; R 0.058 for No 959; in the case of the &#946;-form of (3), crystals are monoclinic, P21/n, a 6.828(2), b 15.464(3), c 10.770(3) &#506;, &#946; 98.58(4)°, Z 2. In (1) and (3&#945;,&#946;), the molecules all lie disposed about crystallographically imposed symmetry elements, with one-half of the molecule, with a substantially planar fused-ring skeleton, comprising the asymmetric unit. In (2), the full molecule is the asymmetric unit; the fused-ring skeletons are substantially planar also, but the molecule exhibits a substantial twist about the bond connecting the two halves, with an interplanar  dlhedral angle of 16.8&#176;. This is ascribed to the steric effect of the large and more numerous t-butyl substituents. 
ER  -

