Vibrational spectrum, conformational stability, barriers to internal rotation, r0 structural parameters and ab initio calculations of bromomethyl methyl ether

Abstract

AbstractThe Raman and far‐infrared spectra at a resolution of 0.10 cm−1 of gaseous bromomethyl methyl ether, BrCH2OCH3, and three of its deuterium isotopes, d2, d3 and d5, were recorded in the 350‐50 cm−1 region. The fundamental asymmetric torsional and methyl torsional modes for the d0 molecule are extensively mixed and were observed at 176 and 130 cm−1, respectively, for the stable gauche conformer with each mode having excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one‐dimensional model the barrier to internal rotation of the methyl moiety is determined to be 549 ± 8 cm−1 (1.57 ± 0.02 kcal mol−1). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500–50 cm−1) spectra of the gas and solid and Raman (3200–10 cm−1) spectra of the gas, liquid and solid is proposed. All of these data are compared with the corresponding quantities obtained from ab initio Hartree‐Fock gradient calculations employing the STO‐3G* basis set. Additionally, complete r0 geometries were determined from the combined previously reported microwave data and CH distances determined from infrared studies along with carbon—hydrogen angles transferred from the corresponding chloride. The heavy atom structural parameters (distance in Å, angles in degrees) are r(C1Br) = 1.996 ± 0.005; r(C1O)=1.359 ± 0.005; r(C2O) = 1.433 ± BrCO = 113.7 ± 0.3; ∢ C1OC2 = 113.5 ± 0.3 and dih BrC1OC2 = 70.9 ± 0.3. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.