Far-Infrared Spectra of Ring Compounds. III. Spectrum, Structure, and Ring-Puckering Potential of Silacyclobutane

Abstract

The infrared spectra of gaseous silacyclobutane and silacyclobutane‐1, ${\text{1‐d}}_2$ have been recorded in the range 24‐300 cm⁻¹. Both molecules show the complicated vibrational fine structure expected from a double‐minimum potential for the ring‐puckering vibration. The absorption maxima of silacyclobutane were fitted to a potential of the form ${\mathrm{V\hspace{0.17em}=\hspace{0.17em}a\hspace{0.17em}(x}}^4{\mathrm{\hspace{0.17em}-\hspace{0.17em}bx}}^2)$ , where $x$ is the ring‐puckering coordinate. The potential barrier is calculated as 440 ± 3 cm⁻¹, and the dihedral angle of the puckered ring as 35.9 ± 2°. The spectrum of silacyclobutane‐1, ${\text{1‐d}}_2$ can be interpreted with the same potential function but the quantitative agreement with observed levels above the barrier is less accurate. The discrepancy is ascribed to interaction between the ring‐puckering mode and the SiD₂ rocking vibration.