Knowledge Bank

Infrared spectra of gaseous and solid cyclobutane and cyclobutane-$d8$ have been recorded from 200 to $4000cm-1$. Raman spectra of both compounds were obtained for the gas, liquid and solid phases. The assignments will be discussed on the basis of the equilibrium configuration, $D2d$. Four gas-phase Raman bands have been observed for the pure ring-puckering mode of $C4H8$ and six for $C4D8$ between 90 and $200cm-1$. These frequencies (as well as ring-puckering frequencies evaluated from combination tones in the mid-infrared spectrum of $C4H8$) were fitted to a potential function of the form V(x) = a($x4-bx2$), where x is the ring-puckering coordinate. The barriers to inversion in $C4H8$ and $C4D8$ are $518\pm 5cm-1$ and $508\pm 8cm-1$ respectively.