Results 1 - 10 of 2167
Results 1 - 10 of 2167. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] The main advances in the chemistry of acetylene in superbasic media achieved over the last five years are analyzed. Particular emphasis is placed on the ethynylation of aldehydes and ketones and C-, N- and O-vinylation. The cascade assembly of complex molecules in which ethynylation and vinylation are consecutive steps is considered. The bibliography includes 369 references
[en] Recently, Lattelais et al. have interpreted aggregated observations of molecular isomers to suggest that there exists a ''minimum energy principle'', such that molecular formation will favor more stable molecular isomers for thermodynamic reasons. To test the predictive power of this principle, we have fully characterized the spectra of the three isomers of C3H2O toward the well-known molecular region Sgr B2(N). Evidence for the detection of the isomers cyclopropenone (c-C3H2O) and propynal (HCCCHO) is presented, along with evidence for the non-detection of the lowest zero-point energy isomer, propadienone (CH2CCO). We interpret these observations as evidence that chemical formation pathways, which may be under kinetic control, have a more pronounced effect on final isomer abundances than thermodynamic effects such as the minimum energy principle
[en] We report measurements of self- and nitrogen-pressure broadening of the P(11) line in the ?1 + ?3 combination band of acetylene at 195 739.649 5135(80) GHz by absorption of radiation emitted by an extended cavity diode laser referenced to a femtosecond frequency comb. Broadening, shift and narrowing parameters were determined at 296 K. For the most appropriate, hard collision, model in units of cm-1/atm, we find 0.146317(27), 0.047271(104) and -0.0070819(22) for the acetylene self-broadening, narrowing and shift, and 0.081129(35), 0.022940(74) and -0.0088913(25) respectively, for the nitrogen-broadening parameters. The uncertainties are expressed as one standard deviation (in parenthesis) in units of the last digit reported. These parameters are 2-3 orders of magnitude more precise than those reported in previous measurements. Similar analyses of the experimental data using soft collision and simple Voigt lineshape models were made for comparison.
[en] Herein, we report on a new multicomponent patterning method based on electrochemically inducible self-assembled monolayers on gold. Two different masked functional groups on monolayers are activated to give amine and acetylene moieties through electrochemical activations at negative potential and positive potential, respectively. The resulting amine and acetylene groups are further used as chemical handles for incorporation of ligand molecules via well-known chemoselective conjugation reactions such as amine-specific conjugation chemistry and click reaction. The chemical conversions of masked functional groups to amine and acetylene groups were characterized by cyclic voltammetry. We demonstrated the orthogonal immobilization of two fluorescent dyes on the patterned surface along the patterned features. Our strategy can provide a useful platform technology for the preparation of multicomponent ligand-patterned substrates with various advantages such as chemical flexibility, mild reaction conditions, and high yields of two orthogonal chemical reactions of amine-specific conjugation and click reaction.
[en] In thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) a nickel atomization tube is placed in the acetylene/air flame on a holder built onto a standard AAS burner head. The liquid to be analyzed is transported by a low or high-pressure pump through a very hot, simple, inexpensive ceramic capillary tip acting as a flame-heated thermospray into the flame furnace. This results in complete sample introduction and increases the residence time of the sample in the absorption volume. This leads for 17 elements to a 3-110-fold improvement in the power of detection compared to conventional flame AAS. The absolute detection limits (3s values, N=25) lie between 0.2 μg l-1 (Zn) and 310 μg l-1 (Se) according to the element. The R.S.D. (N=15) is 1.4-5.5% according to the element and applied concentration. TS-FF-AAS can easily be incorporated on any standard flame AAS instrument and can be automated with a standard autosampler
[en] Highlights: • Ro-vibrational spectrum of C3H4 recorded in 3060–3080 cm−1 region by cw-CRDS. • First detection of the combination band. • Perturbation analysis of the combination band is given. We present the first detection of the high-resolution ro-vibrational spectrum of the combination band of propyne around 3070 cm−1. The fully resolved spectrum is recorded for supersonically jet-cooled propyne using continuous wave cavity ring-down spectroscopy (cw-CRDS). The assignments are supported with the help of accurate ab initio vibration-rotation interaction constants () and anharmonic frequencies. A detailed analysis of the rotationally cold spectrum is given.
[en] Orientation-dependent intermolecular potentials for H2, N2, and C2H2 have been determined on the basis of electron charge density contours, octopolar induction in the dispersion force, electrostatic quadrupolar interaction, and the observed second virial coefficients. The recently settled structure of low-temperature solid acetylene has been discussed. (Auth.)