Carbon molecules, spectroscopic

The cocrystal adduct TTF[Hg3(C6F4)3]2 crystallizes as orange needles by combining 1 1 carbon disulfide methylene chloride solutions of TTF and Hg3(C6F4)3 [56]. As illustrated in Fig. 5, the crystal structure is stabilized by multiple Hg—S secondary interactions which cause the TTF molecules to be sandwiched between two Hg3(C6F4)3 molecules. Spectroscopic and structural results indicate that charge transfer does not occur in this adduct and minimal conductivity is expected. 

We have recently reported the discovery of four strong lines in the infrared and three broader features in the near ultraviolet, observed in absorption spectra of laboratory-produced carbon smoke [9]. The infrared lines have also been noticed by other investigators [10], The aim of this communication is to report new spectroscopic results on isotopically modified samples which support the idea that the reported features in fact originate from a pure and massive carbon molecule which very likely is the soccer-ball-shaped Cm molecule. 

Due to the development of methods for the production of cold cluster beams containing species up to C200, spectroscopic data on all-carbon molecules are now widely available. No direct structural or energetic information is available experimentally, and this has stimulated the application of computational methods in order to evaluate the geometric and electronic structures of these molecules, as well as to predict properties such as ionization potentials and vibrational frequencies. 

Indoles, like pyrroles, are very weak bases typical p a values are indole, -3.5 3-methylindole, -4.6 2-methylindole. -0.3. This means, for example, that in 6M sulfuric acid two molecules of indole are protonated for every one unprotonated, whereas 2-methylindole is almost completely protonated under the same conditions. By NMR and UV examination, only the 3-protonated cation (3//-indolium cation) is detectable it is the thermodynamically stablest cation, retaining full benzene aromaticity (in contrast to the 2-protonated cation) with delocalisation of charge over the nitrogen and o-carbon. The spectroscopically undetectable A -protonated cation must be formed, and formed very rapidly, for acid-catalysed deuterium exchange at nitrogen is 400 times faster than at C-3, indeed the A -hydrogen... 

Organic stractures can be determined accurately and quickly by spectroscopic methods. Mass spectrometry determines mass of a molecule and its atomic composition. NMR spectroscopy reveals the carbon skeleton of the molecule, whereas IR spectroscopy determines functional groups in the molecules. UV-visible spectroscopy tells us about the conjugation present in a molecule. Spectroscopic methods have also provided valuable evidence for the intermediacy of transient species. Most of the common spectroscopic techniques are not appropriate for examining reactive intermediates. The exceptions are visible and ultraviolet spectroscopy, whose inherent sensitivity allows them to be used to detect very low concentrations for example, particularly where combined with flash photolysis when high concentrations of the intermediate can be built up for UV detection, or by using matrix isolation techniques when species such as ortho-benzyne can be detected and their IR spectra obtained. Unfortunately, UV and visible spectroscopy do not provide the rich structural detail afforded by IR and especially H and NMR spectroscopy. Current mechanistic studies use mostly stable isotopes such as H, and 0. Their presence and position in a molecule can... 

It is the use of LIDAR devices as tools for spectroscopic measurements on the various gases present in the atmosphere which concerns us here. These include ozone, carbon dioxide, the CFCs (chlorofluorocarbons, such as CFC-11, trichlorofluoromethane, and CFC-12, dichlorodifluoromethane, used as refrigerants) and all those molecules regarded as atmospheric pollutants. 

Nuclear magnetic resonance, NMR (Chapter 13 introduction) A spectroscopic technique that provides information about the carbon-hydrogen framework of a molecule. NMR works by detecting the energy absorptions accompanying the transitions between nuclear spin states that occur when a molecule is placed in a strong magnetic field and irradiated with radiofrequency waves. 

The molecule S12, like Se, is of Dsd symmetry but in the soHd state it occupies sites of the much lower C211 symmetry [163]. Due to the low solubihty and the thermal decomposition on melting only solid state vibrational spectra have been recorded [2,79]. However, from carbon disulfide the compound Si2-CS2 crystallizes in which the S12 molecules occupy sites of the high Sg symmetry which is close to 03a [163]. The spectroscopic investigation of this adduct has resulted in a revision [79] of the earher vibrational assignment [2] and therefore also of the earlier force constants calculation [164]. In Fig. 24 the low-temperature Raman spectra of S12 and Si2-CS2 are shown. 

Symmetrical cyanine dyes, because of the resonance shown in Figure 6.4 (in which the two contributing structures are exactly equivalent), are completely symmetrical molecules. X-ray crystal structure determinations and NMR spectroscopic analysis have demonstrated that the dyes are essentially planar and that the carbon-carbon bond lengths in the polymethine chain are uniform. The colour of cyanine dyes depends mainly on the nature of the terminal groups and on the length of the polymethine chain. The bathochromicity of the dyes is found to increase... 

Fichter and Kern O first reported that uric acid could be electrochemically oxidized. The reaction was studied at a lead oxide electrode but without control of the anode potential. Under such uncontrolled conditions these workers found that in lithium carbonate solution at 40-60 °C a yield of approximately 70% of allantoin was obtained. In sulfuric acid solution a 63% yield of urea was obtained. A complete material balance was not obtained nor were any mechanistic details developed. In 1962 Smith and Elving 2) reported that uric acid gave a voltammetric oxidation peak at a wax-impregnated spectroscopic graphite electrode. Subsequently, Struck and Elving 3> examined the products of this oxidation and reported that in 1 M HOAc complete electrochemical oxidation required about 2.2 electrons per molecule of uric acid. The products formed were 0.25 mole C02,0.25 mole of allantoin or an allantoin precursor, 0.75 mole of urea, 0.3 mole of parabanic acid and 0.30 mole of alloxan per mole of uric acid oxidized. On the basis of these products a scheme was developed whereby uric acid (I, Fig. 1) is oxidized in a primary 2e process to a shortlived dicarbonium ion (Ha, lib, Fig. 1) which, being unstable, under-... 

Fig. 5.2 Radial distribution curves, Pv

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