Low-energy electron-impact excitation spectra of acetylene

Low-energy (0–5 V above threshold) electron-impact excitation spectra and a transmission spectrum are presented for acetylene. It is found that excitation via temporary negative ions plays a dominant role. Assignments are suggested for the observed electronic excitation processes.     

Reaction of 1,3- hydroxylamino oximes with formaldehyde,acetaldehyde, and acetone

The products of condensation of 1,3-hydroxylamino oximes with formaldehyde have 1-hydroxy-1,2,5,6-tetrahydropyrimidine 3-oxide (cyclic form) structures, the products of condensation with acetone have N-(3-oximino-substituted)-,-dimethylnitrone (open form) structures, and the products of condensation with acetaldehyde exist in solution in the form of a tautomeric mixture of the open and cyclic forms. The products of condensation of alkyl-aromatic 1,3-hydroxylamino oximes with acetaldehyde have N-(3-oximino-substituted)--nitrone (open form) structures.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 252–258, February, 1977.     

Determination of force fields for formaldehyde,acetaldehyde and acetone by the CNDO/force method

CNDO/Force calculations have been done for formaldehyde, acetaldehyde and acetone, and the theoretical force fields evaluated. Experimental force fields are obtained from vibrational frequencies using the least-squares refinement method. The initial force fields considered are based on the bending and interaction force constants obtained from the CNDO/Force calculations and the stretching force constants transferred from chemically related molecules. Vibrational frequencies of H₂CO, D₂CO, HDCO, H₂¹³CO and D₂¹³CO for formaldehyde, CH₃CHO, CH₃CDO, CD₃CHO, CD₃CDO and CH₂DCHO for acetaldehyde, and CH₃COCH₃ CD₃COCH₃ and CD₃COCD₃ for acetone are employed in the force field refinements. The final force fields obtained are found to be reasonable with respect to the diagonal and interaction force constants.     

Polarization of formic acid, acetone, and acetaldehyde

The molar deformation polarizations of formic acid, acetone, and acetaldehyde in the liquid state at 20°C were calculated.     

Ab initio n-electron valence state perturbation theory study of the adiabatic transitions in carbonyl molecules: formaldehyde, acetaldehyde, and acetone

The application of the recently developed second-order n-electron valence state perturbation theory (NEVPT2) to small carbonyl molecules (formaldehyde, acetaldehyde, and acetone) is presented. The adiabatic transition energies are computed for the singlet and triplet n-->pi(*), pi-->pi(*), and sigma-->pi(*) states performing a full geometry optimization of the relevant states at the single state CASSCF level and taking into account the zero point energy correction in the harmonic approximation. The agreement with the known experimental values and with previously published high level calculations confirms that NEVPT2 is an efficient tool to be used for the interpretation of molecular electronic spectra. Moreover, different insight into the nature of the excited states has been obtained. Some of the transitions presented here have never been theoretically computed previously [(3)(pi-->pi(*)) and (3)(sigma-->pi(*)) adiabatic transitions in acetaldehyde and acetone] or have been studied only using moderate level (single reference based) ab initio methods (all adiabatic transitions in acetaldehyde). In the present work a consistent disagreement between NEVPT2 and experiment has been found for the (3)(pi-->pi(*)) adiabatic transition in all molecules: this result is attributed to the low intensity of the transition to the first vibrational levels of the excited state. The n-->pi(*) singlet and triplet vertical transition energies are also reported for all the molecules.     

Laser-assisted electron-impact excitation of hydrogen and helium atoms

The excitation of H(1s–2s) and He(1¹ S–2¹ S) by electron impact in the presence of a nonresonant laser field is studied in the framework of the perturbation theory. The wavelength variation of the total cross section is presented at incident electron energies of 100 eV and 200 eV for hydrogen and 200 eV for helium. The use of pseudostates as intermediate states in the study of excitation of hydrogen is also investigated.     

Low energy,variable angle electron-impact excitation of 1,3,5-hexatriene

A mixture of cis and trans 1,3,5-hexatriene has been studied by electron impact at incident electron energies of 20 eV, 40 eV, 50 eV, and 70 eV, at scattering angles from 0° to 80°, and with effective energy resolutions in the range from 0.05 eV to 0.15 eV. Singlet → triplet transitions with maximum intensities at 2.61 eV and 4.11 eV are observed. The lowest energy spin-allowed excitation which can be detected is the electric dipole-allowed $\text{X}$¹ A_g → 1 ¹B_u transition (in the notation appropriate for the trans isomer). No evidence has been found for a spin-allowed but symmetry-forbidden $\text{X}$¹ A_g → 2 ¹A_g excitation in the vicinity of 4.4 eV transition energy. Many other spin-allowed excitations are observed in the 6–11 eV energy-loss region, and the correlation between these features and those observed in high resolution ultraviolet absorption spectra and other electron-impact spectra is discussed.     

Excretion of formaldehyde, malondialdehyde, acetaldehyde and acetone in the urine of rats in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin, paraquat, endrin and carbon tetrachloride.

Formaldehyde (FA), acetaldehyde (ACT), malondialdehyde (MDA) and acetone (ACON) were simultaneously identified in urine, and their excretion quantitated in response to chemically induced oxidative stress. Urine samples of female Sprague-Dawley rats were collected over dry ice and derivatized with 2,4-dinitrophenylhydrazine. The hydrazones of the four lipid metabolic products were quantitated by high-performance liquid chromatography on a Waters 10-microns mu-Bondapak C18 column. The identities of FA, ACT, MDA and ACON in urine were confirmed by gas chromatography-mass spectrometry. An oxidative stress was induced by orally administering 100 micrograms/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin, 75 mg/kg paraquat, 6 mg/kg endrin or 2.5 ml/kg carbon tetrachloride to rats. Urinary excretion of FA, ACT, MDA and ACON increased relative to control animals 24 h after treatment with all xenobiotics. The system has wide-spread applicability to the investigation of altered lipid metabolism in disease states and exposure to environmental pollutants.     

Conformations of triplet carbonyl compounds: Formaldehyde, acetaldehyde, propionaldehyde and acetone

A conformational study on the lowest triplet states of formaldehyde, acetaldehyde, propionaldehyde and acetone has been done using a minimal basis set, within the unrestricted Hartree—Fock framework.For the C₃H₆O species, the energy hypersurfaces (E θ₁, θ₂, θ₃) were generated, where energy is a function of the methyl rotations (θ₁, θ₂) and C---O out-of-plane bending for acetone, and a function of methyl rotation (θ₁), C₂H₅---C rotation (θ₂) and CHO out-of-plane deformation (θ₃) for propionaldehyde.The analysis of the hypersurface equations revealed the location and relative energies of the critical points (minima, first and second order saddle points as well as maxima): the barriers to inversion at the carbonyl group were 2.7 kcal mol⁻¹ for acetone and 4.2 kcal mol⁻¹ for propionaldehyde. Partial geometry optimization reduced these barriers to 2.5 and 2.4 kcal mol⁻¹ respectively.For comparison, both the pyramidal minimum and planar saddle point for the inversion of triplet formaldehyde and acetaldehyde were totally optimized; the resultant barriers were 2.0 kcal mol⁻¹ and 2.3 kcal mol⁻¹, respectively. The barrier to rotation about the bond to the α-carbon was 1.1 kcal mol⁻¹ for pyramidal acetone, 1.0 for acetaldehyde and ranged from 0.8 to 1.8 kcal mol⁻¹ for the various propionaldehyde conformers.     

Low-energy,low-temperature mass spectra. 5-alkanals

The low-energy, low-temperature mass spectra of thirteen alkanals are reported and their predominant modes of fragmentation discussed in terms of energetics. Characteristic of this class of compounds is the very high proportion of odd-electron ions in the mass spectra, namely [M ? C_MH_2m]^+˙, [M ? H₂O]^+˙ and [M ? H₂O ? C_mH_2m]^+˙.     

Charge reversal of the enolate ions of acetaldehyde and acetone

Collisionally activated charge reversal of HCOCH₂^? and CH₃COCH₂^? produces positive ions whose fragments differ from those of other [C₂H₃O]⁺ ions formed by fragmentation of positive molecular ions, including the [C₂H₃O]⁺ ions from 2,2-dichlorethanol, considered formerly to have the HCOCH₂⁺ structure. The fragmentations of the charge reversed ions are concordant with the RCOCH₂⁺ structures. Least-squares correlations of the collisional activation spectra [C₂H₃O]⁺ are probed as a useful guide to claiming similarity or dissimilarity of ionic structure.     

A theoretical investigation of the plausibility of reactions between ammonia and carbonyl species (formaldehyde, acetaldehyde, and acetone) in interstellar ice analogs at ultracold temperatures

We have reexamined the reaction between formaldehyde and ammonia, which was previously studied by us and other workers in modestly sized cluster calculations. Larger model systems with up to 12H(2)O were employed, and reactions of two more carbonyl species, acetaldehyde and acetone, were also carried out. Calculations were performed at the B3LYP/6-31+G** level with bulk solvent effects treated with a polarizable continuum model; limited MP2/6-31+G** calculations were also performed. We found that while the barrier for the concerted proton relay mechanism described in previous work remains modest, it is still prohibitively high for the reaction to occur under the ultracold conditions that prevail in dense interstellar clouds. However, a new pathway emerged in more realistic clusters that involves at least one barrierless step for two of the carbonyl species considered here: ammonia reacts with formaldehyde and acetaldehyde to form a partial charge transfer species in small clusters (4H(2)O) and a protonated hydroxyamino intermediate species in large clusters (9H(2)O, 12H(2)O); modest barriers that decrease sharply with cluster size are found for the analogous processes for the acetone-NH(3) reaction. Furthermore, if a second ammonia replaces one of the water molecules in calculations in the 9H(2)O clusters, deprotonation can occur to yield the same neutral hydroxyamino species that is formed via the original concerted proton relay mechanism. In at least one position, deprotonation is barrierless when zero-point energy is included. In addition to describing the structures and energetics of the reactions between formaldehyde, acetaldehyde, and acetone with ammonia, we report spectroscopic predictions of the observable vibrational features that are expected to be present in ice mixtures of different composition.     

Highly sensitive and selective catalytic determination of formaldehyde and acetaldehyde

A highly sensitive, simple and selective kinetic method was developed for the determination of ultra-trace levels of formaldehyde and acetaldehyde based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine (DPD) with hydrogen peroxide. The reaction was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of DPD at 510nm, within 30s of mixing the reagents. The optimum reaction conditions were: 20mmolL(-1) DPD, 250mmolL(-1) H(2)O(2), 150mmolL(-1) phosphate, 150mmolL(-1) citrate and pH 6.60+/-0.05 at 25 degrees C. Following the recommended procedure, formaldehyde and acetaldehyde could be determined with linear calibration graphs up to 0.50 and 1.4microg mL(-1) and detection limits, based on the 3S(b)-criterion, of 0.015 and 0.035microg mL(-1), respectively. In addition, analytical data for other 10 aldehydes were also presented. The high sensitivity and selectivity of the proposed method allowed its successful application to rain water, mainstream smoke (MSS) and disposed tips of smoked cigarettes (DTSC). A sample aliquot was directly analyzed for its total water-soluble aldehyde content. A second sample aliquot was heated at 80 degrees C for 10min to expel acetaldehyde and the aliquot was analyzed for its content of other water-soluble aldehydes (expressed as formaldehyde equivalent), and acetaldehyde was determined by difference. The analytical results were in excellent agreements with those obtained following the standard HPLC method based on pre-column derivatization with 2,4-dinitrophenylhydrazine. Moreover, published catalytic-spectrophotometric methods for the determination of aldehydes were reviewed.     

The electron-impact mass spectra of 1,2-benzisoxazole N-oxides

The mass spectra of a new class of heterocyclic N-oxides are reported. It is proposed that the fragmentation processes proceed either by an initial deoxygenation, and or an impact-induced isomerisation, prior to fragmentation. Substituents on the carbocyclic ring normally confer stability on the m olecular ions, whereas those on the heterocyclic ring open up additional fragmentation modes. A phenyl group at the 3-position allows an intramolecular oxygen transfer prior to fragmentation.     

Determination of trace amounts of formaldehyde in acetone

A method to quantify sub-ppm levels of formaldehyde in acetone has been developed and it is reported here. In this method, the different reactivities and stabilities of sulfite with formaldehyde and acetone are used to separate the two carbonyl compounds. Sulfite reacts with formaldehyde to form hydroxymethanesulfonate (HMS), the non-volatile and stable nature of which allows its separation from bulk acetone solvent. The resulting HMS is then converted back to formaldehyde under basic conditions, and formaldehyde is derivatized with 2,4-dinitrophenylhydrazine (DNPH) and quantified in its DNP hydrazone form using high-performance liquid chromatography-UV detection. The method detection limit at the 99% confidence level was 0.051 mg L⁻¹. A batch of samples can be processed within 4 h. The method has been applied to quantify the amount of formaldehyde in an analytical-grade acetone and in a commercial nail polish remover and the level of formaldehyde was found to be 0.175 and 0.184 mg L⁻¹, respectively.     

Low-energy,low-temperature mass spectra: 4—Saturated alkylamines

Electron impact mass spectra obtained with 12.0 eV ionizing electrons at a source temperature of 350 K are reported for 32 saturated alkylamines. The abundances of molecular ions and primary daughter ions are discussed in energetic terms, and the effects of extending the alkyl chain or methylation of the nitrogen atom are considered. A contrast is found between the spectra of amines and those of the analogous alcohols and ethers.