ELECTRON-DIFFRACTION STUDY OF THE MOLECULAR-STRUCTURE AND CONFORMATION OF GASEOUS CHLOROACETONE

The structure and conformation of chloroacetone (CH2Cl-COCH3) has been determined from gas-phase electron diffraction data at 322 K. The majority of the molecules have a gauche conformation with an O = C-C-Cl torsion angle of phi-g = 138 (7)-degrees. Only a small potential hump of V0 = 0.2 (2) kcal/mol separates the two equivalent gauche forms. Small amounts of a syn conformer (phi-s = 0-degrees), where C-Cl is eclipsing C = O, may also be present; our least-squares refinement gave a mole fraction of the syn form of alpha-s = 0.05 (8). Results obtained for the bond distances (r(g)) and valence angles (angle-alpha) are <r(C-H)> = 1.109 (7) angstrom, r(C = O) = 1.216 (3) angstrom, r(CH2Cl-CO) = 1.537 (18) angstrom, r(CH3-CO) = 1.507 (16) angstrom, r(C-Cl) = 1.787 (3) angstrom, angle CH2Cl-C = O = 121.5 (16)-degrees, angle C-C-C = 119.5 (9)-degrees, angle C-C-Cl = 113.7 (9)-degrees, angle C2-C3-H = 110.0-degrees (assumed), angle C2-C1-H = 107 (3)-degrees, angle H-C1-H = 109.0-degrees (assumed). The results are compared with those from related molecules and with results from ab initio calculations.