4 ISOMERIC DIOXOLANE DERIVATIVES OF D-CAMPHORQUINONE

The bicyclo[2.2.1]heptane unit is essentially invariant in all four st ructures, reflecting its rigid nature. The four isomers (1S,2S,4R,4'S) -, (1S,2S,4R,4'R)-, (1S,2R,4R,4'R)- and -one-2-spiro-2'-(4'-chlorometh yl-1',3'-dioxolane), C13H19ClO3, have different positions of substitut ion by the CH2Cl group in the ethylene segment of the dioxolane ring. In each case, this ring has an envelope conformation but the identity of the flap atom varies. All four molecules have a similar overall sha pe and hence give similar packing patterns, resulting in close corresp ondence or simple relationships for the four sets of unit-cell paramet ers and the space groups of the structures.