The puzzle of bond length variation in substituted cyclobutenes. A new example: molecular structure and conformations of 1,2-dimethoxy-3,3,4,4-tetrafluorocyclobut-1-ene.

The structure and composition of 1,2-dimethoxy-3,3,4,4-tetrafluorocyclobut-1-ene (DMCB) have been measured by electron diffraction from the gas at a temperature of 370 K with the help of auxiliary data from molecular orbital and normal coordinate calculations, the former at several levels of theory and basis-set size, most importantly B3LYP/cc-pVTZ. The compound was found to exist primarily as a rotamer of C(s) symmetry (ca. 98%; 2sigma = 11%) with the remainder one of C(2v) symmetry; theory predicts about 88% C(s).

Molecular structure and conformation of chloronitromethane as determined by gas-phase electron diffraction and theoretical calculations.

The molecular structure of chloronitromethane was studied in the gas phase at a nozzle-tip temperature of 373 K. The experimental data were interpreted using a dynamic model where the molecules are undergoing torsional motion governed by a potential function: V = V2/2x(1 - cos 2tau) + V4/2x(1 - cos 4tau) with V2 = 0.81(30) and V4 = 0.

Molecular structures and compositions of trans-1,2-dichlorocyclohexane and trans-1,2-difluorocyclohexane in the gas phase: an electron-diffraction investigation.

The structures and compositions of gaseous trans-1,2-dichloro- (DCCH) and trans-1,2-difluorocyclohexane (DFCH), each of which may exist with the halogen atoms in a diaxial (aa) or diequatorial (ee) conformation, have been investigated by electron diffraction. The analysis was aided by rotational constants from microwave spectroscopy for the ee form of DFCH and by ab initio and density functional theory molecular orbital calculations for all species. The skeletons of the molecules have similar parameter values, but for the Cl-C-C-Cl and F-C-C-F fragments there are significant differences between the corresponding C-C-X bond angles and the X-C-C-X torsion angles in the two systems.

1,2-Dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3): conformational structure and vibrational properties by gas-phase electron diffraction, infrared and Raman spectroscopy, and ab initio molecular orbital and density functional theory calculations.

The molecular structure and conformational properties of 1,2-dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3) have been investigated using gas-phase electron diffraction (GED) data recorded at a temperature of 100 degrees C, together with ab initio molecular orbital (MO) and density functional theory (DFT) calculations, infrared (IR) and Raman spectroscopy in the liquid and solid phases, and normal coordinate analysis (NCA). The molecule exists in the gas- and liquid phases as a mixture of three conformers, gauche(-) [G(-)], with a refined torsion angle phi(BrCCBr)=-71(6) degrees, anti [A], with a torsion angle phi(BrCCBr) approximately -170 degrees , and gauche(+) [G(+)], with a torsion angle phi(BrCCBr) approximately +70 degrees . The second torsion angle of importance, the rotation about the CSi bond, has been refined to a value of +175(13) degrees .

Chalcogenide-halides of niobium (V). 1. Gas-phase structures of NbOBr(3), NbSBr(3), and NbSCl(3). 2. Matrix infrared spectra and vibrational force fields of NbOBr(3), NbSBr(3), NbSCl(3), and NbOCl(3).

The molecular structures of NbOBr(3), NbSCl(3), and NbSBr(3) have been determined by gas-phase electron diffraction (GED) at nozzle-tip temperatures of 250 degrees C, taking into account the possible presence of NbOCl(3) as a contaminant in the NbSCl(3) sample and NbOBr(3) in the NbSBr(3) sample. The experimental data are consistent with trigonal-pyramidal molecules having C(3)(v)() symmetry. Infrared spectra of molecules trapped in argon or nitrogen matrices were recorded and exhibit the characteristic fundamental stretching modes for C(3)(v)() species.