SYNTHESIS AND CRYSTALLOGRAPHY OF 1,2,3,4,6,7-HEXACHLORONAPHTHALENE AND 1,2,3,5,6,7-HEXACHLORONAPHTHALENE

1,2,3,4,6,7-Hexachloronaphthalene (5) and 1,2,3,5,6,7-hexachloronaphthalene (6) have been synthesized via reductive dehalogenation of octachloronaphthalene by lithium aluminium hydride. The reduction proceeds via the substitution of one of the chlorine atoms in an alpha-position and the formation of 1,2,3,4,5,6,7-heptachloronaphthalene (4). The two sterically more crowded alpha-positions (positions four and five) in the heptachloronaphthalene were found to be preferentially reduced as the reduction proceeds. Only trace amounts of other isomers were formed. Crystal and molecular structure of the two title isomers were determined by single crystal X-ray diffraction methods. The compounds crystallize in the space group P2(1)/c with the following cell dimensions: 5, a = 14.71(2) angstrom, b 3.828(4) angstrom, c = 20.45(3) angstrom and beta = 87.8(1)-degrees; 6, a = 9.381(4) angstrom, b = 3.807(2) angstrom, c 16.168(8) angstrom and beta = 102.40(4)-degrees. The structures were determined by direct methods and the obtained models containing a total of 95 parameters for 5 and 48 parameters for 6 were refined by full-matrix least-squares calculations that gave a final R value of: 5, 0.0619 for 486 unique reflections with I/sigma(I) greater-than-or-equal-to 3 and 6, 0,0592 for 382 unique reflections with I/sigma(I) greater-than-or-equal-to 3.