Crystallographic study and molecular orbital calculations of thiadiazole derivatives. Part 3: 3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide, 3,4-diphenyl-1,2,5-thiadiazolidine 1,1-dioxide and 4-ethoxy-5-methyl-3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide

Single-crystal X-ray diffraction studies are reported for 3,4-diphenyl-1,2, 5-thiadiazoline 1,1-dioxide (I), 3,4-diphenyl-1,2,5-thiadiazolidine 1,1-dio xide(II) and 4-ethoxy-5-methyl-3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide (III). Ab initio MO calculations on the electronic structure, conformation and reactivity of these compounds are also reported and compared with the X-ray results. A charge sensitivity analysis is performed on the results ap plying concepts derived from density functional theory, obtaining several s ensitivity coefficients such as the molecular energy, net atomic charges, g lobal and local hardness, global and local softness and Fukui functions. Wi th these results and the analysis of the dipole moment and the total electr on density and electrostatic potential maps, several conclusions have been inferred about the preferred sites of chemical reaction of the studied comp ounds. (C) 2001 Elsevier Science B.V. All rights reserved.