CONFORMATIONAL-ANALYSIS .20. A GAS-PHASE ELECTRON-DIFFRACTION AND AB-INITIO MOLECULAR-ORBITAL INVESTIGATION OF 3-CHLORO-PROPAN-1-OL

The composition of gaseous 3-chloropropan-1-ol at 115 degrees C and 36 7 degrees C, and the molecular structures of the rotational conformers have been investigated by electron diffraction aided by results from ab initio (HF/6-31G) molecular orbital calculations. The mole fractio ns of the two conformers capable in principle of forming intramolecula r O-H ... Cl hydrogen bonds was found to be only 0.04 (14) and 0.05 (2 4) at the lower and higher temperatures, in good agreement with the th eoretical prediction of 0.017 at 0 K, but substantially less than that estimated from an earlier electron diffraction study. Our result stan ds in contrast to that for 2-chloroethanol where the gauche conformer dominates the vapor-phase composition, presumably in large part becaus e of intramolecular hydrogen bonding. The parameter values of 3-chloro propan-1-ol are unexceptional. Some of the more important ones (r(g)/A ngstrom, angle(alpha)/deg) at 115 degrees C with estimates of 2 sigma uncertainties are [r(C-C) = 1.527 (5), r(C-0-C) = 1.547 (12), r(C-C-Cl )=1.497(12), (r(C-H)=1.099 (9), r(C-O)= 1.424 r(6), r(C-Cl)=1.803 (4), angle(C-O-H)=107.3 (assumed), angle(C-C-Cl)= 111.6 (11), [angle(C-C-C )+ angle(C-C-O)]/2 = 110.3 (11), angle(C-C-C)-angle(C-C-O)=3.7 (assume d); assumed values are from the theoretical calculations. (C) 1997 Els evier Science B.V.