Conformational Analysis with Carbon−Carbon Coupling Constants. A Density Functional and Molecular Mechanics Study

For a 1,3-dimethylated model compound ( 1 ), 3 J CC coupling constants were calculated by a density functional (SOS-DFPT/IGLO) method using molecular mechanics as well as ab initio optimized geometries. Boltzmann averaging of the calculated coupling constants for individual conformers resulted in good agreement with the experimental data. The comparison to calculated values allows a more quantitative interpretation of the experimental coupling constants for the conformational analysis of open chain compounds.