Molecular Structure and Conformational Composition of 2-Chloro-1-phenylethanone, ClH₂CC(O)Ph, Obtained Using Gas-Phase Electron-Diffraction Data and Results from Theoretical Calculations

Abstract

The structure and conformation of 2-chloro-1-phenylethanone, ClH(2)C-C(=O)Ph (phenacyl chloride), have been determined by gas-phase electron diffraction (GED), augmented by results from ab initio molecular orbital calculations, employing the second-order Møller-Plesset (MP2) level of theory and the 6-311+G(d) basis set. The molecules may exist as a mixture of different conformers with the C-Cl bond either syn (torsion angle phi = 0 degrees ) or gauche to the carbonyl bond. At 179 degrees C, the majority of the molecules (90 +/- 11%) have the gauche conformation (phi = 112(3) degrees). Torsion is also possible about the C-Ph single bond. Both experimental and theoretical data indicated, however, that the phenyl ring is coplanar or nearly coplanar with the carbonyl group. The results for the principal distances (r(g)) and angles (angle(alpha)) for the gauche conformer from a combined GED/ab initio study (with estimated 2sigma uncertainties) are the following: r(C-C)(phenyl) = 1.394(2) (average value) A, r(C(phenyl)-C(carbonyl)) = 1.484(5) A, r(C(carbonyl)-C(alkyl)) = 1.513(5) A, r(C-Cl) = 1.790(5) A, r(C=O) = 1.218(6) A, r(C-H)(phenyl) = 1.087(9) (average value) A, r(C-H)(alkyl) = 1.090(9) A (average value), angle C(phenyl)-C=O = 119.5(9) degrees, angle C(phenyl)-C(carbonyl)-C(alkyl) = 119.2(10) degrees, angle C-C-Cl = 109.8(12) degrees, angle C(2)-C(1)-C(carbonyl) = 122.8(15) degrees, angle C-C(alkyl)-H = 111.2 degrees (ab initio value).

Molecular structure and conformational composition of methyl chloroacetate: An electron-diffraction and ab initio molecular orbital investigation

“…For methyl chloroacetate this is in good agreement with the ab initio results. It is close to the value observed for R = Ph [3]. Since Ph is larger than OCH3 this indicates that steric repulsion is not the only factor determining the value of this torsion angle.…”

“…Since Ph > CH 3 > H, we may expect the ClACAC@O torsion angle to decrease from R = H to R = Ph. This is indeed what is observed, the ClACAC@O torsion angle is 180°in chloroacetaldehyde [1], 139(7)°in chloroacetone [2] and 112(7)°in 2-chloro-1-phenyletanone [3]. When R = Cl or R = OCH 3 we have two bond dipoles on the terminal carbon atom.…”

“…Among these are molecules with the general formula ClH 2 CAC(@O)R, where R = H, CH 3 , a phenyl group or a Cl atom [1][2][3][4]. In these compounds conformers where CACl and C@O have different positions relative to each other have been observed.…”

Molecular structure and conformation of phenylacetyl chloride as obtained by gas-phase electron diffraction and theoretical calculations

“…The phenyl group can rotate around the CAC phenyl bond and it would be of interest to see the value of this torsion angle as well. Earlier we have also published results for 2-chloro-1-phenylethanone where X = Cl and Y = phenyl [4].…”