Molecular Structure, Equilibrium Conformation, and Ring-Puckering Motion in 1,1,3,3-Tetramethylcyclobutane. An Electron-Diffraction Investigation Augmented by Molecular Orbital and Normal Coordinate Calculations.

The molecule cyclobutane (CB) has a nonplanar carbon skeleton folded around a line connecting diagonally opposite atoms. The puckering angle (the change from planarity) of ∼30° is generally attributed to steric repulsion between the four sets of adjacent methylene groups that would be opposed in a planar ring and is relieved by the puckering. According to this criterion, a similar molecule, 1,1,3,3-tetramethylcyclobutene (TMCB), in which adjacent methylene groups do not exist, would be expected to have a planar ring in the equilibrium form.

Molecular structure and conformations of 1,2-dimethoxycyclobutene-3,4-dione. An electron-diffraction investigation augmented by quantum mechanical and normal coordinate calculations.

The structure and conformations of 1,2-dimethoxycyclobutene-3,4-dione in the vapor at a temperature of 185 °C have been measured by gas-phase electron diffraction. The molecule exists in two forms, one of symmetry C2v with the methyl groups trans to the double bond, and one of Cs symmetry with a methyl group cis and the other trans to this bond (these forms hereafter designated as trans and cis). The molar ratio trans/cis is 68/32 with a 2σ uncertainty of about 24.

1,4-Cyclohexanedione. Composition, molecular structures, and internal dynamics of the vapor: an electron diffraction investigation augmented by molecular orbital calculations.

Electron diffraction experiments on the vapor of 1,4-cyclohexanedione have been carried out at a nominal temperature of 435 K. The results are consistent with the presence of a mixture of a chair form of C2h symmetry and a twisted boat form of D2 symmetry. The former has the familiar dynamic properties of a semirigid molecule, but the D2 form undergoes a large-amplitude twisting motion (pseudorotation) that degrades the symmetry to C2.

High-resolution infrared and electron-diffraction studies of trimethylenecyclopropane ([3]-radialene).

Combined high-resolution spectroscopic, electron-diffraction, and quantum theoretical methods are particularly advantageous for small molecules of high symmetry and can yield accurate structures that reveal subtle effects of electron delocalization on molecular bonds. The smallest of the radialene compounds, trimethylenecyclopropane, [3]-radialene, has been synthesized and examined by these methods. The first high-resolution infrared spectra have been obtained for this molecule of D3h symmetry, leading to an accurate B0 rotational constant value of 0.

Structure and torsional properties of oxalyl chloride fluoride in the gas phase: an electron-diffraction investigation.

The structure and torsional properties of oxalyl chloride fluoride in the gas phase have been measured by electron diffraction at temperatures of 22, 81, 158, and 310 °C. The molecule may be regarded as a hybrid of oxalyl chloride and oxalyl fluoride. Since the former exists as a more stable periplanar anti form (ϕ = 180°) in equilibrium with a less stable gauche form (ϕ ≃ 60°) and the latter as an equilibrium between two periplanar forms, anti and syn, the second form of oxalyl chloride fluoride is an interesting question.

Conformational analysis. 24. Structure and composition of gaseous oxalyl fluoride, C(2)F(2)O(2): electron-diffraction investigation augmented by data from microwave spectroscopy and molecular orbital calculations.

The molecular structure and composition of gaseous oxalyl fluoride (OXF) has been investigated by electron diffraction (GED) at nozzle-tip temperatures of -10, 149, and 219 degrees C. The GED data were augmented by molecular orbital calculations, and the analysis was aided by use of rotational constants from microwave (MW) spectroscopy. As in the other oxalyl halides, there are two stable species, of which the more stable is periplanar anti (i.