MOLECULAR-STRUCTURE AND CONFORMATIONAL COMPOSITION OF 2-CHLOROPROPANOL, A GAS-PHASE ELECTRON-DIFFRACTION AND AB-INITIO INVESTIGATION

Gas-phase electron diffraction (ED) data obtained at 72-degrees-C together with results from ab initio calculations have been used to determine the structure and conformational composition of 2-chloropropanal. The majority (66 +/- 26%) of the molecules have a conformation where the CH3 group is eclipsing the C=O bond (C-C-C=O torsion angle angle phi1 = 27 (7)degrees). Smaller amounts of a form (23 +/- 28%) where H is eclipsing C=O (angle phi1 = 109 (20)degrees) and a form (11 +/- 26%) where Cl is eclipsing C=O (angle phi1 = 240-degrees) probably also is present in the gas phase. These results for the conformational composition are in fairly good agreement with the ab initio results calculated at the MP2/6-31G*//HF/6-31G* level. The results for the principal distances (r(g)) and angles (angle(alpha)) from a combined ED/ab initio study for the conformer where CH3 is eclipsing C=O, with estimated 2sigma uncertainties, are r(C-H)methyl = 1.115 (10) angstrom, r(C-CO) = 1.529 (4) angstrom, r(C-CH3) = 1.527 (4) angstrom, r(C=O) = 1.205 (4) angstrom, r(C-Cl) = 1.805 (6) angstrom, angle C-C-H(methyl) = 110.4-degrees (ab initio value), angle H-C-Cl = 108.1 (39)degrees, angle OC-C-Cl = 108.9 (7)degrees, angle C-C-C = 112.4 (15)degrees, angle C-C=O = 124.3 (18)degrees, and angle C3-C2-Cl = 109.2 (7)degrees.