Trimethylene Oxide. II. Structure, Vibration-Rotation Interaction, and Origin of Potential Function for Ring-Puckering Motion

Abstract

Calculation of Raman intensities for the ringpuckering vibrations of trimethylene oxide and cyclobutane. The importance of electrical anharmonicityIn the previous paper of this series, the microwave spectra of four isotopic species of trimethylene oxide were investigated and the potential function for the puckering of the four-membered ring was determined. Further analysis of the data has now enabled the molecular structure to be calculated. The structural parameters deduced from the rotational constants are: r(C-C) = 1.549±0.OO3 A, r(C-O) = 1.449±0.OO2 A, r(C,,-H,,) = 1.091± 0.002 A, r(Cp-H~)=1.100±0.OO3 A,

Determination of the structure of methylene cyclobutane confirming a non-planar ethene and the structure of the argon–methylene cyclobutane van der Waals complex

“…Stroyer-Hansen and Norby-Svendsen [12] studied the far infrared spectrum of MCB observing an unusually large number of Dv = 1, 2, 3 and 4 transitions for the ring puckering vibration as high as v = 10. They also derived ring-puckering potential in a reduced coordinate system, X and P X as derived by Chan et al [6], and a barrier of 139 cm À1 . A good fit required addition of an X 6 term to the potential function.…”

“…They measured the a component of the dipole moment in the inversion states, 0.514 D, but the out of plane transition c-type moment was too small to determine. The ring-puckering potential function was derived from the inversion frequency and the vibrational dependence of the rotational constants using the reduced coordinate potential function derived by Chan et al [6]. The barrier to inversion of the ring was 160 ± 40 cm À1 .…”

Decomposition Mechanism of 1,2-Dioxetane

“…It has only two pairs of hydrogen-hydrogen interactions, compared to eight for cyclobutane, with the remaining interactions involving lone-pair electrons on the oxygens. The comparison of cyclobutane with trimethylene oxide (17) shows the latter is planar with no barrier to ring puckering by 17" in the ground state (18). This planar structure of trimethvlene oxide indicates a weaker interaction for lone-pairs, which one might expect as lonepairs are rather diffuse for long-range interactions.…”

Infrared Band Progressions in the CH2 Scissoring Region and the Ring Puckering Vibration of Trimethylene Oxide and some Deuterated Analogs

“…we can use the geometrical parameters determined by Chan et al (6) to estimate the principal moments of inertia. We find that all molecules are near oblate symmetric tops with the axis of the greatest moment of inertia, the C axis, being perpendicular to the molecular plane.…”