ELECTRON-DENSITY DISTRIBUTION IN FLUOROBENZENE DERIVATIVES

The electron-density distribution in four fluorobenzene derivatives has been studied at 120 (2) K. Mo Kalpha radiation was used throughout (lambda = 0.71073 angstrom). 1,5-Difluoro-2,4-dinitrobenzene, C6H2F2N2O4, (I), M(r) = 204.1, orthorhombic, Pbca, a = 10.804 (3), b = 13.007 (4), c = 10.381 (2) angstrom, V = 1458.8 (7) angstrom3, Z = 8, D(x) = 1.86 Mg m-3 mu = 0.178 mm-1, F(000) = 816, R = 0.034 for 2581 unique reflections with multipole refinement. 4-Fluorobenzoic acid, C7H5FO2, (II), M(r) = 140.1, monoclinic, P2(1)/n, a = 26.733 (5), b = 6.2947 (9), c = 3.7257 (6) angstrom, beta = 94.88 (2)-degrees, V = 624.7 (2) angstrom3, Z = 4, D(x) = 1.49 Mg m-3, mu = 0.121 mm-1, F(000) = 288, R = 0.037 for 1710 reflections. 4-Fluorobenzamide, C7H6FNO, (III), M(r) = 139. 1, monoclinic, P2(1)/a, a = 9.584(2), b = 7.601(3), c = 8.903(2) angstrom, beta = 92.67 (3)-degrees, V = 647.9 (3) angstrom3, Z = 4, D(x) = 1.43 Mg m-3, mu = 0.109 mm-1, F(000) = 288, R = 0.049 for 1529 reflections. 3-Chloro-4-fluoroaniline, C6H5ClFN, (IV), M(r) = 145.6, orthorhombic, Pbca, a = 14.608 (5), b = 15.757 (6), c = 5.303 (2) angstrom, V = 1220.6 (8) angstrom3, Z = 8, D(x) = 1.59 Mg M-3, mu = 0.538 mm-1, F(000) = 592, R = 0.039 for 2090 reflections. The deformation densities on the halogen-carbon bond axes were investigated, based on the oriented-atom model. The electron accumulation on the C-F bond is sharper than that on the C-Cl bond, indicating the more compact distribution of the 2p orbitals of the F atom compared to the 3p orbitals of the Cl atom. The pronounced positive effective charge of the carboxylic H atom of (II) was estimated by kappa refinement and molecular orbital calculations.