Theoretical calculations, far-infrared spectra and the potential energy surfaces of four cyclic silanes

- Ab initio calculations do an excellent job of matching experimentally determined ring-puckering potential functions.
- The spectra for the hindered pseudorotation of two cyclic silanes were well fit with periodic potential energy functions.
- Results from ab initio calculations are in very good agreement with experimentally determined conformational energies.

Theoretical computations have been carried out to calculate the potential energy functions for the out-of-plane vibrations of four cyclic silanes, and the results were compared to experimental functions determined from far-infrared data. The experimental and computed ring-puckering potential functions for 1-silacyclopent-3-ene, which are in excellent agreement, are quartic in nature with tiny barriers to planarity. Similarly, the calculated and experimental potential functions for 1,3-disilacyclopent-3-ene are nearly identical. For silacyclopentane and 1,3-disilacyclopentane the calculations predict ring-twisitng barriers of 2493 cm−1 (vs. 2110 cm−1 observed) and 1395 cm−1, respectively. The conformational energies for the bent forms were calculated to be 1467 cm−1 (vs. 1509 cm−1 observed) for the former and 878 cm−1 for the latter relative to the energy of the twist minima. One-dimensional hindered pseudorotational potential energy functions were found to work well for predicting the observed far-infrared spectra for the bending (pseudorotational) vibration.