CATEMERIC HYDROGEN-BONDING IN (+)-ENDO-CAMPHORCARBOXYLIC AND (+/-)-ENDO-CAMPHORCARBOXYLIC ACID

4,7,7-Trimethyl-3-oxobicyclo[2.2.1]heptane-2-endo-carboxylic acid (I), (+)-C11H16O3, M(r) = 196.246, monoclinic, P2(1), a = 10.712 (3), b = 6.724 (3), c = 7.136 (3) angstrom, beta = 95.07 (3)-degrees, V(234 K) = 512.0 (4) angstrom 3, Z = 2, D(m)(295 K) = 1.25 (1), D(x)[295 K; V = 515.0 (5) angstrom 3] = 1.266 g cm-3, lambda-(Mo K-alpha) = 0.71069 angstrom, mu = 0.98 cm-1, F(000) = 212, T = 234 (1) K, R = 0.058 for 638 observed reflections. (II), (+/-)-C11H16O3, M(r) = 196.246, monoclinic, P2(1)/c, a = 10.849 (2), b = 6.751 (3), c = 14.248 (2) angstrom, beta = 94.96 (1)-degrees, V(252 K) = 1039.6 (5) angstrom 3, Z = 4, D(m)(295 K) = 1.24 (1), D(x)[295 K; V = 1046.0 (6) angstrom 3] = 1.246 g cm-3, lambda-(Mo K-alpha) = 0.71069 angstrom, mu = 0.96 cm-1, F(000) = 424, T = 252 (1) K, R = 0.065 for 1290 observed reflections. In both the (+)-enantiomer (I) and the racemate (II) the crystal is composed of single-strand helical chains parallel to the b axis, produced by infinite repetition of a hydrogen bond linking the carboxylic acid of one molecule with the ketone of an adjacent screw-related molecule, so that each hydrogen-bonding helix contains molecules of only one chirality. The packing in (II), whose c cell dimension is doubled relative to (I), corresponds to stacked pairs of (P2(1)) cells packed as in (I), with alternating chirality in the c direction.