Chemistry and crystal structures of tetrabenzoylethylene, its photolysis product and tetraacetylethylene

X-ray crystallographic analysis has revealed that the light-sensitive form (A) and the light-stable form (A) of tetrabenzoylethylene are not valence tautomers but are two crystalline modifications of the same substance. The difference in the stability of these forms to light appears to be a consequence of their different molecular conformations and packing in the solid state. The molecular conformation of the A form is represented by (8) and that of the A’ form by (9). The related tetraacetylethylene has the conformation (10) in the solid state. X-ray crystallographic analysis has also revealed that the photolysis product (B) of tetrabenzoylethylene is 4-phenoxy-3, 4, 6-triphenyl-1H, 4H-furo[3, 4-c]- furan-l-one (11). The crystal structures of (8), (9), (10) and (11) were determined by X-ray diffraction: diffractometer data at 295 K were refined by least-squares techniques to residuals of 0·064 (2161 ‘observed’ reflections) for (8), 0·057 (1310) for (9), 0·049 (1295) for (10) and 0·061 (1639) for (11). Crystals of (8) are monoclinic, P2₁/n, a 8·775(5), b 17·352(9), c 30-985(8)Å, β 93·01(3)°, Z 8. Crystals of (9) which contain carbon disulfide are monoclinic, A2a, a 21·21(2), b 6·181(4), c 20·35(2)Å, β 102·77(7)°, Z 4. Crystals of (10) are monoclinic, P2₁/n, a 7·540(2), b 4·392(2), c 14·770(4) Å, β 96·29(2)°, Z 2. Crystals of (11) are monoclinic, P2₁/n, a 14·820(4), b 15·000(3), c 10·819(4) Å, β 106·02(2)°, Z4.