The effects of fluorine and chlorine substitution on bond lengths in ethanes and disilanes: comparisons of ab initio and experimental information

An investigation of the structure and bond rotational potential of some fluorinated ethanes by NMR spectroscopy of solutions in nematic liquid crystalline solvents

“…The bond length obtained of 1.373 Å is between those calculated by the DFT and MP2 methods, and is within the range of values obtained for other fluorinated alkanes [24], and the percentage found for the trans conformer of 73% is very close to that calculated of 74% by the MP2 method. The value obtained for h 412 from the NMR data of 115.5°is significantly larger than the value of 112.3°cal-culated by the DFT method, which may be a genuine difference between these two methods of obtaining the structure, or it may originate from a contribution of J aniso If it is assumed that the DFT geometry is correct, but the rotational potential is changed by dissolving the molecule in the liquid crystalline solvent, then differences between observed and calculated dipolar couplings reveal contributions of the anisotropies in spin-spin coupling.…”

“…The large values of D aniso 17 and D aniso 24 for the two-bond compared with the one-bond C-F couplings could simply reflect the relatively small magnitudes of D 17 and D 24 . Thus, although both J aniso ij and D ij values depend on the molecular ordering, the tensors J aniso ij and D ij do not have the same principal axes, and this means that it is possible for J aniso ij to remain finite when D ij is zero.…”

Infrared and Quantum-Chemical Studies of Dimethylsilane

“…In order also to improve the precision of the B3LYP calculations, a fine grid consisting of 99 radial shells round each atom and 302 angular points in each shell was employed. Under these conditions, bond lengths were reproducible to 0.00005Å or better (24). The need for four-decimal-place precision in identifying small differences in bond lengths has been emphasized earlier (18).…”

Quantum-Chemical Studies of Fluoroethanes: Vibrational Assignments, Isolated CH Stretching Frequencies, Valence Force Constants, and Bond Length Relationships

“…For monofluoroethane additional calculations were carried out with the 6-31G* basis set and at the MP2 level as detailed elsewhere. 39 In all cases the "tight" condition for optimization in the Gaussian input was employed togther with an SCF convergence limit of 10 -10 . Test runs showed that under these conditions CH and CF bond lengths converged from differing starting geometries to final values agreeing to within 0.000 02 Å, for the CC bond, the corresponding figure was 0.000 05 Å.…”

“…However, with DFT-based force fields, where the scale factors are in any case (39). f From the re(HF/tz) correlation with ν is CH(obs) for CH type bonds only.…”