Microwave Spectrum of Acetyl Chloride

Abstract

The microwave spectrum of ten isotopic species of acetyl chloride are reported. Internal rotation of the methyl group splits some of the rotational transitions into doublets in addition to the chlorine hyperfine structure. Analysis of the internal rotation splitting gives a barrier to internal rotation of 1296±30 cal! mole. From the hyperfine structure, the chlorine nuclear quadrupole coupling constants for CI36 along the C-Cl bond axis and perpendicular to the plane of symmetry of the molecule were determined to be -58.5 and 21.5 Me, respectively. The corresponding values for CP7 were -46.4 and 17.2 Me. These coupling constants have been interpreted to give information about the double bond and ionic character of the C -Cl bond. The follow-ing structural parameters have been determined from the rotational constants of CILCOCI36, CILCOCI37, CI3ILCOCI36, CHzC 13 0CI35, CILC018CI36, and CD z COCp6:

The gas phase characterization of perfluorobutyryl chloride, C3F7COCl, using chirped pulse Fourier transform microwave spectroscopy

“…To summarize we find that ethanoyl chloride [1,2] and propionyl chloride [3,4] have been studied at high resolution. In these studies spectroscopic constants including chlorine nuclear quadrupole coupling tensors were determined together with barriers to methyl rotation of 1296 ± 30 cal mol À1 and 2480 ± 40 cal mol À1 , respectively.…”

The pure rotational spectrum of pivaloyl chloride, (CH3)3CCOCl, between 800 and 18800MHz

“…The generic distances for acyl chlorides are slightly less than 1.79 Å [1][2][3]. This varies a bit from the 1.77 Å given for a standard carbon-chlorine bond [12], although the slightly longer distance is close to the ab initio value (to be discussed later).…”

“…From internal rotations to torsional strain, spectroscopy of all kinds has dominated the field with regards to characterizing these molecules. Of these simple acyl chlorides, acetyl, propionyl, and butyryl chloride have been observed using microwave spectroscopy [1][2][3][4], but pivaloyl chloride, (CH 3 ) 3 CCOCl, has not. However, far-infrared work of pivaloyl chloride did provide values on the barriers to internal rotation [5].…”

“…It has an asymmetry parameter, j, of À0.630 calculated from ab initio calculations at the MP2/6-311+G(3d,3p) level [7]. One might also anticipate internal rotation in accordance with other molecules in its class [1][2][3][4][5][8][9][10]. These types of qualities in a molecule can quickly begin to complicate spectra and increase the difficulty of assigning spectra.…”

The microwave spectrum, harmonic force field, structure, and dipole moment of propiolyl chloride

“…The molecules include the acid fluorides and acid chlorides of formic acid (1, 2), acetic acid (3,4), cyclopropanecarbox ylic acid (5,6), and propionic acid (7,8). A logical and interesting extension is to the corresponding derivatives of propiolic (propynoic) acid, one of the simplest planar carboxylic acids.…”