Rotational and vibrational spectra, conformational stability, potential functions and ab initio calculations of methacryloyl chloride

Abstract

The microwave spectrum of CH 2C(CH 3)C 35ClO has been recorded from 12.4 to 39.0 GHz. Both a- and b-type transitions were observed and an R-branch assignment has been made for the s-trans conformer. The rotational constants were found to have the following values: A=4785.13±0.06, B=2248.74±0.01, and C=1551.54±0.01 MHz. From a diagnostic least-squares adjustment to fit the three rotational constants, and with reasonable carbon—hydrogen bond distances and angles, the following heavy atom skeletal structural parameters were obtained: r(CCl)=1.792±0.008 Å, r(CO) = 1.191 (fixed), r(CCH 3) = 1.509 (fixed), r(CCClO) = 1.492±0.007 Å, r(CC) = 1.342 (fixed), ∠ CCCl = 116.1±1.1°, ∠ CCCClO = 122.7 (fixed), < CCCH 3 = 123.9 (fixed), and ∠ CCO = 123.9±1.5°. The quadrupole coupling constants for the s-trans conformer have the following values: χ aa = −44.9, χ bb = 20.4, and χ cc = 24.5 MHz. The infrared (IR) (3500-20 cm −1) and Raman spectra (3500-10 cm −1) have been recorded for both the gaseous and solid phases of methacryloyl chloride. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis of a more stable s-trans and high-energy s-cis conformational equilibrium for the fluid phases. The potential functions governing internal rotation of both the CClO and CH 3 tops have been determined from the far-IR spectrum of the gas. The asymmetric potential function, conformational energy difference, and optimized geometries have also been obtained from ab initio calculations at both the 3–21G* and 6–31G* basis-set levels. A normal-coordinate analysis has also been performed with a force field determined from the 3–21G* basis set. All of these results are compared to corresponding quantities for some similar molecules.