The molecular structure, conformation, potential to internal rotation and force field of 2-chloro-2,2-difluoroacetamide applying gas electron diffraction, quantum chemical calculations and two different methods of vibrational corrections

2-Chloro-2,2-difluoroacetamide has been studied by electron diffraction (BD ) and ab initio Hartree-Fock (HF) calculations with 6-31G* and 6-311 + + G* * basis sets and DFT calculation with a 6-311 + + G** basis set. The ab ini tio calculations predict one conformation with the C-Cl bond approximately orthogonal to the CCON skeleton and a slightly nonplanar NH2 group. Two different methods for calculation of vibrational corrections have been used, and their influence on the determination of the structure parameters has been discussed. A molecular force field has been determined, and the ca lculated fundamental frequencies have been tentatively assigned. The struct ural parameters were refined using ab initio results as constraints in the analysis. The structural parameters obtained using the curvilinear approach are: r(g)(N-H-4) = 1.048(4), r(g)(C=O) = 1.214(1), r(g)(C-N) = 1.366(4), r (g)(C-C) = 1.568(2), r(g)(C-Cl-7) = 1.771(2), r(g)(C-F-8) = 1.350(2), angle OCN = 125.8(2), angle CCN = 114.5(3), angle CCF8 = 110.7(1), angle Cl7CF8 = 109.0(1), angle CNH4 = 114.1(9). Bond distances are in Angstrom and bond angles in degrees. Uncertainties are one standard deviation from least-squa res refinement using a diagonal weight matrix and inclusion of the uncertai nty in the electron wave length. The barrier heights when the C-Cl is syn (alpha = 0) and anti (alpha = 180) to the C-N bond are of the order of 8.9(9) and 5.0(5) kJ/mol respectively, with a minimum at 96(6)degrees. The theoretical calculations are in good a greement with the experimental results. (C) 1999 Elsevier Science B.V. All rights reserved.