Tandem mass spectrometry of aminated fullerene derivatives

The products of the reaction between fullerenes (C₆₀/C₇₀) and dimethylamine were investigated by fast atom bombardment (FAB) mass spectrometry and tandem mass spectrometry (MS/MS). The FAB mass spectrum shows peaks corresponding to the addition of up to eight dimethylamine species, exclusively to C₇₀. MS/MS reveals an unusual fragmentation pattern. The mass spectrum of the reaction products, together with a number of tandem mass spectra, are shown.     

The vibrational spectrum and structure of trifluorotrichlorodisiloxane

The vibrational spectrum of trifluorotrichlorodisiloxane (F₃SiOSiCl₃) is reported, analyzed and assigned in terms of a linear C_3v model, by comparison with that of structurally related hexachlorodisiloxane (Cl₃SiOSiCl₃). This is the first assignment of the vibrational spectrum for this molecule. The vibrational spectrum of Cl₃SiOSiCl₃ is assigned on the basis of a linear D_3d model, which is different from a bent C_2v model in the previous literature.     

Silyl‐functionalized Silsesquioxanes: New Building Blocks for Larger Si‐O‐Assemblies,including the First Si‐Si‐Bonded Silsesquioxanes

Novel silyl‐functionalized silsesquioxane building blocks have been prepared by treatment of Cy₇Si₇O₉(OH)₃ ( 1 , Cy = c‐C₆H₁₁) with hexachlorodisilane or hexachlorodisiloxane, respectively, in the presence of triethylamine. Reactions in a 1:1 molar ratio afforded the trichlorosilyl‐functionalized silsesquioxane derivatives Cy₇Si₈O₁₂SiCl₃ ( 2 ) and Cy₇Si₈O₁₂OSiCl₃ ( 3 ). Related bis(silsesquioxanes), (Cy₇Si₈O₁₂)₂ ( 4 ) and (Cy₇Si₈O₁₂)₂O ( 5 ) are accessible in a similar manner by employing a 2:1 molar ratio of the reactands. Compound 1 also served as a starting material in the preparation of the partially closed silsesquioxane cages Cy₇Si₇O₁₁(OH)SiMe₂ ( 6 ) and Cy₇Si₇O₁₁(OH)Si(OEt)₂ ( 7 ), while the related condensation product Cy₇Si₇O₁₀(OSiMe₃) ( 9 ) was made by AlCl₃‐catalyzed elimination of water from Cy₇Si₇O₉(OH)₂OSiMe₃ ( 8 ). The molecular structure of 9 was determined by X‐ray diffraction.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

The role of distonic ions in the formation of CH3NH 3 + and (CH3)2NH 2 + from the molecular ions of octopamine and synephrine

It is shown by mass-analyzed ion kinetic energy spectrometry that the metastably decomposing molecular ions of octopamine (p-HOC₆H₄CH(OH)CH₂NH₂) and synephrine (p-HOC₆H₄CH(OH)CH₂NHCH₃) yield only protonated methylamine and dimethylamine, respectively, as product ions. From deuterium labeling and variation of the internal energy of the molecular ions, experimental support has been obtained that these product ions are generated via the occurrence of a distonic ion-neutral complex. In the case of octopamine, this complex would consist of a nitrogen-protonated aminomethyl radical and p-hydroxylbenzaldehyde in which the former species abstracts the aldehydic or phenolic hydrogen atom from the latter to give protonated dimethylamine.     

Kinetics and products of the gas-phase reactions of O3 with amines and related compounds

The kinetics and products of the gas-phase reactions of O₃ with a series of aliphatic amines and related compounds have been investigated at 298 ± 2 K and 740 Torr total pressure of air. The absolute rate constants obtained (in cm³ molecule^-1 s^-1 units) were: methylamine, (7.4 ± 2.4) x 10^-21; dimethylamine, (1.67 ± 0.20) x 10^-18; trimethylamine, (7.84 ± 0.87) x 10^-18; 2-(dimethylamino)ethanol, (6.76 ± 0.83) x 10^-18; and tetramethylhydrazine, (5.21 ± 0.60) x 10^-18. The major products observed from the O₃ reactions with the use of in situ FT-IR absorption spectroscopy were: from trimethylamine, (CH₃)₂NCHO, CH₃N=CH₂ and HCHO; and from dimethylamine, CH₃N=CH₂, CH₃NO₂, and HCHO. Possible reaction mechanisms are presented and discussed.     

Sol–gel derived Si/C/O/N‐materials: molecular model compounds,xerogels and porous ceramics

Polymeric Si/C/O/N xerogels, with the idealized polymer network structure comprising [Si O Si(NCN)₃]_n moieties, were prepared by reactions of hexachlorodisiloxane (Cl₃Si O SiCl₃) with bis(trimethylsilyl)carbodiimide (Me₃Si NCN SiMe₃, BTSC). NMR and FTIR spectra indicate the existence of ‐NCN‐ and Si O Si‐ units in the xerogels and also in the ceramic materials obtained upon pyrolysis. The feasibility of this reaction protocol was confirmed on the molecular level by the deliberate synthesis of the macrocyclic compound [SiPh₂ O SiPh₂(NCN)]₂, the crystal structure and spectroscopic data of which are reported. The influence of pyridine as a catalyst for the cross‐linking reaction was studied. The degree of cross‐linking increased within the polymers with the addition of pyridine. It was shown by the reaction of hexachlorodisiloxane with excess pyridine that the latter appears to activate only one out of the two ‐SiCl₃ moieties under formation of hexacoordinated silicon compounds. The crystal structure of Cl₃Si O SiCl₃(pyridine)₂ is presented. Quantum chemical calculations are in support of this adduct being a potential intermediate in the pyridine catalyzed sol–gel process. The ceramic yield after pyrolysis of the Si/C/O/N‐xerogels at 1000 °C, which reaches values up to 50%, was found to depend on the aging protocol (time, temperature), whereas no correlation was found with the amount of pyridine added for xerogel synthesis. The Si/C/N/O‐ceramics obtained after pyrolysis at 1000 °C under NH₃ are completely amorphous. Chemically they have to be considered as hybrids between an ideal [SiOSi(NCN)₃]_n network and glass‐like Si₂N₂O. The products are mesoporous with closed pores and a broad pore size distribution. Copyright © 2011 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies on some 2-substituted 1,3-dithi a-2-boracyclopentanes

Infrared and Raman spectra are reported for 2-X-1,3-dithia-2-boracyclopentanes, where X = Br, Cl, Ph or NMe₂. In all cases the vibrations of the heterocyclic ring unit can be assigned in terms of C₂ symmetry, corresponding to a “twisted-ring” conformation similar to that found for the related molecule 1,3-dithiolan-2-thione. The internal modes of the B-Ph unit are in agreement with C_2v “local” symmetry, while those for B-NMe₂ suggest a considerably lower symmetry.     

High-resolution solid-state 11B and 13C MAS NMR of icosahedral carboranes

The globular-shaped icosahedral carboranes, o-, m-, and p-C₂B₁₀H₁₂, yield high-resolution ¹¹B and ¹³C MAS solid-state NMR spectra. Chemical shifts and linewidths are comparable to those of solution spectra. Spin—lattice relaxation times indicate the quadrupolar mechanism to be dominant for the B-11 relaxation. Linewidths of spectra recorded at 96 MHz and 64 MHz were similar. At 298 K, the ¹³C T₁ of p-carborane was found to be an order of magnitude smaller than those of the other two isomers. This can be attributed to the higher phase transition temperature of p-carborane indicative of the stronger intermolecular dipolar CH interactions made possible by the para-carbon vertices. Substitution on o-carborane by a methyl group yields spectra of comparable linewidths to those of the parent compound. Substitution by a bulkier phenyl group, however, results in extensive broadening of both ¹¹B and 13C signals of the derivative 1-Ph-o-C₂B₁₀H₁₁.     

Fluorine-containing β,β-disubstituted trimethylsilyl vinyl ethers: synthesis and reactions with N-(1,1,2,2-tetrafluoroethyl)dimethylamine

Fluorine-containing β,β-disubstituted trimethylsilyl vinyl ethers prepared by hydrosilyla-tion of appropriate substituted trifluoromethylketenes react with N-(1,1,2,2-tetrafluoro-ethyl)dimethylamine to give β,β,β’,β’-tetrasubstituted divinyl ethers. Conditions for selective hydrofluorination of tert-butyl perfluoro-2-methylpent-2-enoate into the corresponding saturated ester were developed. Pyrolysis of the latter with P₂O₅ afforded perfluoromethyl-(propyl)ketene.     

Low-frequency vibrations of molecular solids: XV. Globular molecule 1,2-dichloroethane

The far infrared and Raman spectra of polycrystalline 1,2-dichloroethane and 1,2-dichloroethane-d₄ for the low temperature modification have been measured from 450 to 33 cm⁻¹ at various temperatures from −100 to −182°C. Raman spectra of the high temperature crystalline modification for both samples were also investigated. The Raman data are in conflict with those previously reported. Assignments are made for the lattice vibrations in terms of the crystallographic unit cell C_2h⁵ (P_21/c) with two molecules per unit cell. The spectra of the high temperature modification are consistent with those expected for orientationally disordered crystals.     

A dihydrogen bond between a bridging hydride and the NH proton of a coordinated dimethylamine: solid state, solution and theoretical characterization

The addition of one equivalent of dimethylamine (DMA) to the 44 valence-electron triangular cluster anion [Re₃(μ₃-H)(μ-H)₃(CO)₉]⁻ (1) affords the novel unsaturated derivative [Re₃(μ-H)₄(CO)₉(DMA)]⁻ (2, 46 valence electrons) which contains a dimethylamine molecule terminally coordinated to a cluster vertex. Theoretical calculations (DFT) reveal that in the more stable conformation the dimethylamine NH proton is directed towards the hydride bridging the opposite cluster edge in syn position, the close proximity of the ligands bound to the cluster surface allowing the formation of an unconventional N-H ? (μ-H)Re₂ hydrogen bond. The presence of this conformation in the solid state has been proven by an X-ray structural analysis of crystalline [PPh₄]2. Spectroscopic evidences (IR and NMR) indicate that the dihydrogen bond is maintained also in solution and, by the evaluation of the proton spin-lattice relaxation rates at variable temperature, a good estimate of the H ? H distance in solution has been determined.     

Comparative infrared study of hydrogen-bonded heterodimers formed by HCl,DCl, HF and DF with (CH3)2O,CH3OH and (CH3)3COH in the gas phase. Assignment of vibrational band structure in (CH3)2O… HCl

Observation of v_s bands in the infrared spectra of some O…H-Cl and O…H-F dimers and their deutero derivatives completes the investigation of a series of twelve related dimers. Comparison is made with related spectra, and arguments are advanced in favour of the earlier assignment of the band structure in the spectrum of (CH₃)₂O… H-Cl.     

Infrared intensities of liquids XXII: Optical and dielectric constants, molar polarizabilities, and integrated intensities of liquid benzene-d6 at 25 °C between 5000 and 450 cm–1

This paper presents accurate infrared absorption intensities of liquid benzene-d₆ at 25?°C, between 5000 and 450 cm^–1. The results are presented as graphs and tables of the real, n, and imaginary, k, refractive index spectra, which are also called the optical constant spectra. The real refractive index is shown between 8000 and 450 cm^–1. The absolute errors in the k values are estimated to be ～3% below, and up to 60%, above, 4700 cm^–1, with those in the n values ～0.25% throughout. The Beer-Lambert molar absorption coefficient spectra, E _m(?ν), and the complex dielectric constant spectra, ?′(?ν) and ?″(?ν), were calculated from the optical constant spectra. To correct for macroscopic dielectric effects, the complex molar polarizability spectra, α′_m(?ν) and α″_m(?ν), were calculated from the dielectric constant spectra under the Lorentz local field. The properties of bands in these different spectra are compared. The imaginary molar polarizability spectra were fitted convincingly to 208 Classical Damped Harmonic Oscillator bands, and the areas under the corresponding ?να″_m bands gave the integrated intensities C _j . These were assigned as far as possible and are tabulated. The transition dipole moments of well assigned transitions, and for the infrared-active fundamentals, under the double harmonic approximation, the dipole moment derivatives with respect to the normal coordinates, were calculated from the values of C _j , and are presented. This appears to be the first extensive measurement of the infrared absorption intensities of liquid benzene-d₆. The results are compared with literature data for liquid and gaseous benzene-d₆.     

1.2-Bis(pentamethylcyclopentadienyl)tetrachlorodisilane and its reduction to decamethylsilicocene

Reaction of pentamethylcyclopentadienyl(pentachloro)disilane (2), prepared from hexachlorodisilane and potassium pentamethylcyclopentadienide (Cp^*K), with a further equivalent of Cp^*K leads selectively to the title compound Cp^* ₂ Si ₂ Cl ₄ (3) which was characterized by NMR and X-ray structural data. Dehalogenation of 3 with four equivalents of sodium naphthalenide offers an alternative route for the synthesis of decamethylsilicocene (1). Dedicated to Professor Mitsuo Kira on the occasion of being honoured with the Wacker Silicon Award 2005.     

Microwave spectrum,structure, dipole moment and internal rotation of ethyl fluorosilane

Microwave spectra of the trans and gauche isomers of ethyl fluorosilane and their eleven isotopically substituted species have been measured. The r_s structures of the two isomers were determined from the observed moments of inertia. The molecular structures found for the two isomers in the present study are compared with those of analogous molecules. Dipole moments of the two isomers were determined by Stark-effect measurements and are also compared with those of analogous molecules. The energy difference between the trans and gauche isomers was obtained from the relative intensity measurements of the spectra and the barrier to internal rotation of the methyl group for the gauche isomer was obtained from the A—E splittings of the spectra in the first excited methyl torsional state. The V₃ value was 2775 ± 25 cal mol^?1.     

Infrared spectra of some oxides of K2NiF4 and related structures

The i.r. spectra of some Ln₂BO₄ and LnSrBO₄ compounds (Ln = La, Pr, Nd, Sm or Gd;B = Fe, Al, Co or Cu) with K₂NiF₄ or related structures have been studied in the range 800-300 cm⁻¹. The BO₆ octahedra in compounds with K₂NiF₄ structure are elongated. The assignment of the bands in terms of internal modes of sheets of bridged BO₆ octahedra or square-planar BO₄ sheets has been considered. The observed spectra are correlated with those of solid solutions of these oxides and of LnBO₃ perovskites. Unusually high stretching frequencies found in some of the oxides are discussed in terms of the short BO bonds in the basal plane and the LnO bonds along the c axis.     

Infrared spectra and molecular conformation of butyronitrile and methyl thioacetonitrile

The infrared absorption spectra of two related compounds, butyronitrile (CH₃CH₂-CH₂CN) and methylthioacetonitrile (CH₃SCH₂CN) have been examined in the liquid and solid phases. Vapour phase spectra of butyronitrile have also been recorded. Evidence is given for the existence of two rotational isomers trans and gauche, for both compounds. In both cases the energy difference between the two rotamers appears to be small with the gauche form identified as the low energy conformer for butyronitrile. For methylthioacetonitrile it was not possible to determine the more stable rotational isomer.     

Effect of X-ray irradiation on the optical absorption of СdSe1−xTex nanocrystals embedded in borosilicate glass

The effect of X-ray irradiation on the optical absorption spectra of CdSe_1?xTe_x nanocrystals embedded in a borosilicate matrix is studied. The observed blue shift of the absorption edge and bleaching of the confinement-related features in the spectra are related to X-ray induced negative ionization of the nanocrystals with charge transfer across the nanocrystal/matrix interface. The radiation-induced changes are observed to recover after longer post-irradiation storage at room temperature.     

Vibrational spectra and conformational behavior of 1,1- diethylcyclopropane

Infrared spectra (from 4000 to 400 cm⁻¹) of solid, liquid and gaseous 1,1-diethylcyclopropane and Raman spectra of the condensed phases of this compound have been recorded. Evidence for two conformational isomers, one of which vanishes in the polycrystalline solid phase, is found in the spectral data for the liquid phase. It has been concluded that these two rotational isomers are the gauche/gauche conformers which arise when the two methyl groups are displaced in a conrotatory sense (C₂ symmetry) and a disrotatory sense (C_s symmetry) from a hypothetical cis/cis (C_2υ) structure. These conclusions are consistent with the conformational results previously obtained for ethylcyclopropane and ethyloxirane. In addition, from the variable temperature liquid phase Raman intensity measurements, the C₂ rotamer of 1,1- diethylcyclopropane has been calculated to be 1.1 ± 0.2 kcal/mole more stable than the C_s form, and is the sole conformer remaining in the solid phase. Tentative vibrational assignments, in agreement with those for related molecules, are proposed for the major spectral bands of 1,1-diethylcyclopropane.