Equilibrium constants of the conformational interconversion and vibrational analyses of vinylfluorogermanes

The structures of CH₂=CH-GeKL₂, (K=L, L=H for the monofluoro and K=H, L=F for the difluoro derivative of vinylgermane) were investigated by DFT-B3LYP/6-311++G** (Density Functional Theory. Becke-3 exchange and Lee-Yang-Parr correlation functional) and ab initio MP2/6-311++G** (Moller-Plesset perturbation theory of 2^nd order) calculations. The potential functions for the internal rotation of the GeKL₂, rotors were calculated and it was found that they are very similar for the two molecules. Both molecules exhibit a conformational equilibrium between the two stable cis and gauche forms, where in both cases the trans conformation is one of the two transition states. In the case of the vinylmonofluorogermane the gauche form is slightly lower than the cis one while in the case of vinyldifluorogermane the two forms are nearly degenerate. The equilibrium constants of the two equilibria were calculated and are presented. The vibrational frequencies of the two molecules in their stable conformations were computed. The potential energy distributions. PED. among the symmetry co-ordinates of the normal modes of the vinylfluorogermanes were calculated from normal coordinate calculations and a complete assignment of all spectral modes is provided. Further the infrared and vibrational Raman spectra of the two conformational equilibria were plotted and shown in this work. It is pointed out that in contrast to previous findings in a similar system. in the present case DPT total energies seem to be of similar reliability as MP2 ones.