Molecular structure and conformation of gaseous bromoacetyl chloride and bromoacetyl bromide as determined by electron diffraction

Bromoacetyl chloride and bromoacetyl bromide are studied by gas phase electron diffraction at nozzle-tip temperatures of 70°C and 77°C, respectively. Both compounds exist as mixtures of anti and gauche conformers. The mole fraction anti, with uncertainties estimated at 2σ, was found to be 0.474(0.080) for bromoacetyl chloride and 0.615(0.069) for bromoacetyl bromide. The results for the distance (r_a)and angle (∠α) parameters, with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wave length and correlation effects are as follows: (1) bromoacetyl chloride, r(C-H) = 1.086(0.062) Å, r(CO) = 1.188(0.009) Å, r(C-C) = 1.519(0.018) Å, r(C-Cl) = 1.789(0.011) Å, r(C-Br) = 1.935(0.012) Å, ∠C-CO = 127.6(1.3)°, ∠C-C-Cl = 111.3(1.1)°, ∠C-C-Br = 111.0(1.5)°, ∠H-C-H = 109.5°(assumed), $\text{?}$/o (gauche torsion angle relative to 0° for the anti form) = 110.0°(assumed); (2) bromoacetyl bromide, r(C-H) =1.110(0.088) Å, r(C=O) = 1.175(0.013) Å, r(C-C) = 1.513(0.020) Å, r(CO-Br) = 1.987(0.020) Å, r(CH₂-Br) = 1.915(0.020) Å, ∠C-CO = 129.4(1.7)°, ∠CH₂-CO-Br = 110.7(1.5)°, ∠CO-CH₂-Br = 111.7(1.8)°, ∠H-C-H = 109.5°(assumed), ∠ø (gauche torsion angle relative to 0° for the anti form) = 105.0°(assumed). The structural results are discussed in connection with the structures of related molecules.