Molecular structures, conformations, force fields and large amplitude motion of cis-3-chloro-2-propen-1-ol as studied by quantum chemical calculations and gas electron diffraction augmented with quantum chemical calculations on 2-propen-1-ol

Abstract

B3LYP and MP2(F) quantum chemical calculations have been performed for 2-propen-1-ol using the cc-pVTZ basis set. Five stable conformations are detected and related to the two conformations observed experimentally. The calculated normal frequencies are scaled for two conformers and their assignments are compared. Similar quantum chemical calculations predict three stable conformers for cis-3-chloro-2-propen-1-ol. Quantum chemical force field calculations reveal large amplitude motions about the C C bond for all conformers. Least-squares refinements of the gas electron diffraction data using a mixture of two static conformers verify the presence of these two conformers. The agreement with the experimental data for this type of refinements is not satisfactory which indicates that large amplitude models should be used. Describing the torsions about the C C bond as frame work vibrations in harmonic large amplitude angular motion of Gaussian distributions for two conformations improved the agreement with the experimental data considerably. The root-mean-square angular amplitude of the torsions for the two conformations refined to 28.6(12)° and 21.4(46)°, with dihedral angles C C C O equal to −125.5(17)° and 180(fixed)°, respectively. Some r a distances (Å) and r α angles (degrees) obtained are: r(C C) = 1.5044(20), r(C C) = 1.3435(16), r(C O) = 1.4299(14) and r(C Cl) = 1.7366(19), <(C C C) = 125.60(12), <(C C O) = 111.0(2), <(C C Cl) = 123.61(10). Parenthesized values are [ σ 2 lsq + (0.001 × r) 2] 1/2 for bond distances, where σ lsq is the least-squares standard deviation. For the angles σ lsq is given. There is good agreement between the experimental results and the quantum chemical calculations.