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The gas-phase structure of 6,9-CS[B.sub.8][H.sub.12] and 6,9-CN[B.sub.8][H.sub.13] were configured by electron diffraction and ab initio calculations. Results show that the position of the sulfur atom is very close to that of the boron atom occupying the equivalent position in the parent molecule [[B.sub.10][H.sub.14].sup.2-]], reflecting the similarity of sizes of sulfur and boron atoms.

The molecular structures of the three heterodecaboranes arachno-6,9-[C.sub.2][B.sub.8][H.sub.14], arachno-6,9-[N.sub.2][B.sub.8][H.sub.12] and arachno-6,9-[Se.sub.2][B.sub.8][H.sub.10] were determined by ab inito theory and structure of 6,9-[C.sub.2][B.sub.8][H.sub.14] was determined by gas-phase electron diffraction (GED). The additional comparison of the GIAO-HF and GIAO-MP2 method shows that for these heteroborane clusters, electron correlation effects on the computed [delta](11B) values are significant.

The activation energies for the racemization of C3-symmetric complexes of four- and six coordinate metals with hydrotris(methimazolyl)borate lignad are explored by variable-temperature NMR and ab initio calculations. All of the four-coordinate complexes studied are found to follow a dissociative mechanism of racemization with activation energy dependent upon solvent donor ability.

A methodology for the determination of solution structures of small molecules from residual dipolar coupling constants measured in dilute liquid crystals is developed. The study shows that reducing the degree of order by using dilute liquid crystralline media in combination with precise measurement of small residual dipolar coupling constants, is a way of overcoming the limitation of strongly orienting liquid crystals associated with the complexity of 1H NMR spectra for molecules with more than 12 protons.

The molecular structure of tri-tert-butylphosphine imide is re-determined using the DYNAMITE method, which allows all assumptions about local symmetry to be removed without increasing the number of refining structural parameters excessively. The re-determination of the structure using the more advanced methods has reported much shorter P-N bond than was determined, and is consistent with the molecule being regarded as HN=PBu(super t)(sub 3), rather than HN(super -)-P(super +)Bu(super t)(sub 3).

Pnictinyl radicals were spontaneously generated from jack-in-the-box dipnictines in the solid state gas phase.

Research has been conducted on the gallaborane. The characterization of this compound has been carried out via the chemical analysis and its IR and NMR spectra.

Research has been conducted on the monochlorogallane that has been synthesized by gallium(III) chloride metathesis. Physical properties of monochlorogallane are described.

Bis(perfluorovinyl)mercury, Hg(CF==CF(sub.2)(sub.2), is discussed relative to characterization, synthesis and structure in both crystalline and gas phases. Significant variation seen in the C-F bond distances of the CF==CF(2ub.2) group in other work was the motivation for the study. A low-temperature reaction between 2 equivalents of perfluorovinyl lithium, from CF(sub.3)CH(sub.2)F and butyllithium and mercury(II) chloridem gives high yields of Hg(CF=CF(sub.2))(sub.2). Crystals were achieved by slow cooling.

Electron diffraction and ab initio computations at the MP2/631G were used to determine the molecular structure of 3,3-diethylpentane in the gas phase. The molecule is observed to have substantial distortion from regular tetrahedral coordination at the central carbon atom, showing two CCC angles in the D2d form and two angles in the S4 form reduced to 106.7(8) degrees and increased to 110.9(4) degrees, respectively. These distortions are found to have originated from asymmetry of the electron density distribution around the CH2 groups.

Electron diffraction and calculated ab initio were employed in determining the gas phase molecular structure of chlorodifluoronitrosomethane (CClF2NO). CClF2NO theoretically consists of two conformers with symmetries that are near degenerate in energy and separated by a barrier of about 1 kJ mol-1. Calculations reveal that the nitroso group's rotation is barely stemmed over several torsional angle values at room temperature.

A study was conducted to examine the products gas-phase quenched of the completed reactions of B4H10 and ethyne at 70 degrees celsius. Mass spectrometric techniques were utilized to monitor the gas-phase reaction and gas-phase electron diffraction. Results revealed that a wider variety of nido-carboranes and and their derivatives, which were formed by acetylenic C-C and C-H bond cleavages, could be seen after the quenched gas-phase reaction of B4H10 and ethyne.

An optimized synthetic process for alpha,omega-bis(bromosilyl)alkanes, BrH2Si(CH2)nSiH2Br (n = 2,3) is suggested. Reactions of these compounds with isopropylamine produce the heterocycles 1-isopropyl-1-aza-2,5-disilacyclopentane and 1-isopropyl-1-aza-2,6-disilacyclohexane, while the analogous reaction with bi(bromosilyl)methane produces 1,5-diisopropyl-1,5-diaza-2,4,6,8-tetrasilacyclooctane rather than a four-membered ring compound. This shows that compounds with Si-N-N units prefer relatively narrow Si-N-N angles because of beta-donor Si***N interactions.

The gas phase chemical structure of [4]dendralene 3,4-dimethylenehexa-1,5-diene was analyzed by gas-phase electron diffraction (GED) coupled with ab initio computations. The [4]dendralene exhibited a C2 symmetry in the gas phase with butadiene units exhibiting twisted conformations. The [4]dendralene was also characterized as a 2-substituted anti butadiene that exhibited increased steric repulsion in the planar butadiene groups during substitution reactions.

Electron diffraction and ab initio calculations were done to study the gas phase molecular structure of trifluorophosphine tetraborane(8), B4H8PF3. The results fit the properties of a model of the gas as consisting only of the endo conformer in Cs symmetry with the PF3 group staggered in relation to the B(1)-H(1) bond. At the MP2/TZP//MP2/TZP + ZPE(HF/6-31G*) level, the exo conformer was predicted to represent about 2% of the compound vapor which is in accordance with the nuclear magnetic resonance spectrum obtained.

The Cs symmetry of the ground state of the P(NMe2)3 molecule, with its planar and pyramidal geometries at the nitrogen atoms, is an inherent structural property of compounds containing the P(NR2)3 skeleton and related E(NR2)3 units. This was proven by the good agreement between ab initio calculations and single-crystal x-ray diffraction experiments concerning the crystal structures of P(NMe2)3 and H2C=P(NMe2)3 and the gas-phase structure of H2C=P(NMe2)3.

The molecular structures of gaseous CH3AsF2 and (CH3)2AsF were determined by electron-diffraction experiments and ab initio computations. Findings indicated that both As-C and As-F bond lengths are shortened by increasing numbers of fluorine atoms but that the angles CAsF and FAsF are almost invariant in the series (CH3)3As, (CH3)2AsF, CH3AsF2, and AsF3.

The pyramidal configuration of Si2N-O in silylated nitrogen compounds was investigated in the gas, liquid and solid phases. To this end, O-methyl-N,N-disilylhydroxylamine was synthesized by reacting bromosilane and O-methylhydroxylamine in the presence of 2,6-lutidine. The compound, which explodes when heated to 200 degrees Celsius, was also the subject of ab initio computations. Both experimental and calculated results suggested that the pyramidal nitrogen structure is caused by the repulsion between lone pairs of nitrogen and oxygen electrons.

The synthesis and characterization of the compound 1-phenyl-1,2-dicarba-closo-dodecarborane(12), 1-C6H5-1,2-closo-C2B10H11, are described. A complete assignment of its 11B NMR spectrum has been performed via 11B{1H}/11B{1} (COSY), 1H{11B selective} and 1H{11B}/1H{11} COSY spectroscopy. The orientation of the phenyl ring relative to the carborane gas in the gas and liquid phases has been determined by electron- and X-ray diffraction analyses and ab initio calculations.

A study has been conducted to examine the structure of perfluorocyclopropene, a perfluorinated compound, in gaseous, solution and crystalline states using electron diffraction, rotational spectroscopy and liquid crystal NMR spectroscopy, respectively. X-ray diffraction techniques were also used to measure crystal growth. The structural parameters for the solid and gas phases are presented.

Electron diffraction, ab initio and IGLO computations analyze the molecular structure of 1-(difluoroboryl)pentaborane(9), demonstrating high thermal stability in the gas phase. A difluoroboryl group replaced the apical boron atom of the molecule, which comprised a pentaborane(9) cage. The exo B-B bond was the center of rotation for the BF2 moiety.

Electron diffraction and ab initio calculations analyze the structure of a dimethylene-tetraborane compound, comprising a tetraborane(10) cage. An elliptical conformation characterized the C-C bonding of this molecule, whose symmetry was C2v. The tetraborane(10) cage, situated at specific wing boron atoms, was associated with an ethene moiety.

The structure and conformations of 2-methylacetophenone are examined by ab initio calculations carried out by gas electron diffraction (GED). The studies have shown that the explanation of reactivity by steric inhibition of resonance and by other steric factors is supported by experimental and theoretical investigation of the actual molecular shape.

Gas-phase electron diffraction (GED) and quantum chemical calculations are used for examining the structures of the molecules methylamine-borane, Me[H.sub.2]N.B[H.sub.3], and dimethylamine-borane, [Me.sub.2]HN.B[H.sub.3]. The structural variations and energetics of the gaseous adducts are discussed with respect to the basicity of [Me.sub.n][H.sub.3-n]N fragment and the importance of secondary interactions in the solid adducts is assessed by the semi-classical density sums approach.

(F3C)F2SiONMe2 is a well suited model compound for an investigation of the nature of the bonding forces between Si and N atoms in germinal Si/N systems. (F3C)F2SiONMe2 shows a very strong Si...N interaction, which leads to a Si...N distance shorter than the Si-C bond in the same molecule.

Molecular structures of two carbaboranes, closo-2,3-C2B9H11 and nido-2,9-C2B9H13, are discussed using gas-phase electron diffraction (GED) for the first time. Ab initio computations carried out on 7.8-C2B9H13 (1), geometric data at various levels of theory are presented.

It is revealed that theoretical quantum chemical calculations predicted the molecular structures of the diphosphines and the corresponding radicals. The conformational analyses of all structures found the gauche conformers of the diphosphines with C2symmetry to be the most stable.

The simplest accessible GeON compound H3GeONMe2 was prepared and studied in the gas phase and the solid state. This study was done to assess the influence of the group 14 atom on the molecular structure of the E-O-N units.

Research is presented describing the techniques used to ascertain the bonding levels of (N,N-dimethylanminoxy)trifuorosilane solutions in all forms using molecular geometry.