Structures of 2,6-disubstituted naphthalenes

The crystal structures of 2,6-naphthalenedicarboxylic acid (NDA) and dimeth yl 2,6-naphthalenedicarboxylate (NDC) have been solved ab initio using a co mbination of X-ray powder diffraction and computational chemistry technique s. These two crystal structures, and that of 2,6-dimethylnaphthalene (DMN), have been refined by the Rietveld technique. DMN crystallizes in the ortho rhombic space group Pbca, with a = 7.4544 (4), b = 6.0826 (6), c = 20.0946 (12) Angstrom, V = 911.1 (1) Angstrom(3) and Z = 4. The structure consists of a herringbone stacking parallel to a, resulting in loosely bound layers perpendicular to c. NDA crystallizes in the triclinic space group P (1) ove r bar, with a = 3.7061(8), b 7.4688(14), c = 8.5352(22) Angstrom, alpha = 8 6.62(2), beta = 85.49(2), gamma = 87.99 (2)degrees, V = 235.00 (6) Angstrom (3) and Z = 1. The structure consists of loosely packed hydrogen-bonded cha ins along [1 (1) over bar 1]. NDC crystallizes in the monoclinic space grou p P2(1)/c, with a = 13.41931 (14), b = 6.14869 (5) c = 7.15257 (5) Angstrom , beta = 100.400 (1)degrees, V = 580.47(1) Angstrom(3) at 300 K and Z = 2. The structure consists of layers of NDC molecules perpendicular to a. The e ster group is twisted 20 degrees out of the mean ring plane in NDC. The con formations of the carboxyl groups in NDA and NDC differ. MP2 calculations s uggest that the observed twist in NDC corresponds to an increase in conform ational energy of 9 kJ mol(-1).