Microwave Spectrum, Ring-Puckering Potential Function, and Dipole Moment of Methylenecyclobutane

Abstract

The microwave spectra of methylenecyclobutane in the ground state and in the first six excited states of the ring-puckering vibration have been assigned. The 11=0 state and 11= 1 state are very close in energy and are strongly coupled giving rise to nonrigid-rotor spectra. Analysis shows the energy difference to be 33 592 MHz. This energy difference together with the vibrational dependence of the rotational constants gives the ring-puckering potentialfunction to be 7.65 (X'-9.15X1) em-I where X is a reduced ring-puckering coordinate. This potential function contains a barrier to ring inversion of 160±40 em-I. The a component of the dipole moment is found to be 0.514 D in the ground state and to have the ring-puckering vibrational dependence ~=0.496+0.0051 (XI) •• (debye). 10

Structure, vibrations and relative stability of 1-methylcyclobutene and methylenecyclobutane tautomers using DFT and CCSD methods

“…Experimentally, it was found using mid-IR spectrum, microwave spectrum and Raman spectrum to be 168 AE 10, 160 AE 40 and 141 AE 5 cm À1 , respectively. 16,27,28 Another fundamental ring puckering is located at $ 658 cm À1 , which is in good agreement with the same mode found at 657.2 cm À1 using mid-IR spectrum 16 and con¯rmed by Raman spectrum. 28 The C¼C stretching theoretically located at $ 1770 cm À1 is experimentally observed at 1675 cm À1 (note that the authors did not assign which mode is which).…”

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

“…Dv = 0, had been assigned and fit first by Sharpen et al [5] and then by Charro et al [9] for the parent isotopomer, c-12 C 3 H 6 12 C@ 12 CH 2 .…”

“…The resulting double minimum ring-puckering potential leads to inversion pairs that frequently exhibit large vibration-rotational coriolis type perturbations. The microwave spectrum of methylene cyclobutane (MCB), cAC 3 H 6 C@CH 2 , was originally observed by Sharpen and Laurie [5] in the ground and first six excited states of the ring-puckering vibration. Analyzing the coriolis perturbations of the a-type rotational transitions in the ground inversion pair, they determined the inversion frequency, 1.12051(57) cm À1 .…”

Nematic phase nuclear magnetic resonance studies of the molecular structures of cyclobutanone and methylenecyclobutane

“…The best least squares fit gave a large rms deviation of 10.4 Hz for a rigid planar molecule and this is obviously not an acceptable structure. The value of w was not given in the microwave study (4) and an attempt to determine this parameter was unsuccessful. No value of w would adequately reproduce the dependence of all three rotational constants upon the vibrational level and, therefore, the value found for cyclobutanone, -0.4, was adopted.…”

“…Scharpen and Laurie have studied the microwave spectra of both cyclobutanone (3) and methylenecyclobutane (4). For cyclobutanone a puckering potential was derived which fits both the microwave and far-infrared data (5) potential function has a small barrier of 8 cm-I at the planar position and the ground state lies 9 cm-' above the barrier.…”