Pyrolysis vibrational spectra

The bond dissociation energy D[CFj-CX)—H] = 381 8 kJ mol at 298 K has been derived from data obtained in a study of the kinetics of thermal bromination of trifluoroacetaldehyde," and the results of a detailed study of the vibrational spectrum of the aldehyde have been presented. 2-Bromotetrafluoropropanal has been obtained by pyrolysis of the dibromide prepared from the ether (20-CF3-CF CH-OEt. ... 

An informative IR spectrum of the t-butyl radical, containing 18 bands, has been recorded after freezing of the products of vacuum pyrolysis of azoisobutane [110] and 2-nitrosoisobutane [111] in an argon matrix at 10 K (Pacansky and Chang, 1981). This spectrum is in agreement with a pyramidal structure of the radical (CH3)3C (symmetry C3v) which has elongated CH bonds in positions trans to the radical centre. On the basis of experimental vibrational frequencies and ab initio calculations of the radical geometry the enthalpy value [// (300)] of its formation has been calculated as 44 kJ moP. ... 

The reaction of equimolar amounts of CrOF4 and CsF at 100°C yields orange-brown Cs+CrOF5 , which was characterized by infrared spectroscopy [306], Chromium tetrafluoride oxide combines with NOF in a 1 1 mole ratio to yield the stable, pink solid adduct NO+CrOF5 which was characterized by vibrational spectroscopy [304]. Controlled pyrolysis of NO+CrOF5 yields a mixture of NO+CrOF 5 and NO+CrOF5 -nCrOF4 [304], The infrared spectrum of this mixture... 

Despite the calculated, rather low first ionization potential, suggesting an isolated, easy-to-detect band in the silaethene PE spectrum, numerous pyrolysis experiments with promising precursors, such as 1,3-disilacyclobutane, yielded no reproducible PE band in the expected region. Eventually, in the thermal retrodiene cleavage of a 5,6-bis(trifluoromethyl) derivative of 2-silabicyclo[2.2.2]octa-5,7-diene, a novel band exhibiting vibrational fine structure appeared within the precalculated region (Figure 4). 

A sample (50-60 mg) is hot-pressed at a temperature of 180 C to obtain a film of about 0.05 mm thickness, and the IR spectrum is recorded and compared with standard reference spectra. Difficulties will be encountered in distinguishing between a mixture of PVC and EVA and VC/VA copolymer. The main difference is seen in changes to the C-H stretching vibration bands of PVC in the region of 3030-2900 cm due to the presence of (CH2) units in the polymerised ethylene portion of EVA. Equally difficult to detect is CPE, where the same effect is observed. Pyrolysis/GC and NMR spectroscopy are used as confirmatory techniques, with the latter also being used to quantify some polymeric compounds. 

A prominent example in this context is the recent detection of oxadisulfane (HSOH) via rotational spectroscopy [4]. The successful identification of HSOH among the products of the pyrolysis of (t-Bu)2SO was possible due to accurate predictions of the spectroscopic parameters of HSOH. In fact previous searches for HSOH without such predictions were unsuccessful [4]. As outlined by Winnewisser et al. [4], quantum chemical calculations were used to predict the HSOH rotational-torsional spectrum The equilibrium rotational constants were obtained at the CCSD(T)/cc-pCVQZ level of theory and then augmented by vibrational corrections at the CCSD(T)/cc-pVTZ level. Dipole moment components were also computed in order to predict the type of rotational transitions detectable and their intensity. 

A weak absorption spectrum between 825 and 695 nm was observed by Judge and Moule in the pyrolysis products of dimethyl selenide (CH3)2Se. The carrier was found to be a thermally unstable species and was identified from its band spectrum as selenoformaldehyde. The vibrational fine structure was consistent with that of a singlet-triplet transition. The spectrum was assigned to the a A <- X Aj transition. Glinski et al. recently observed this same electronic transition as a phosphorescence emission spectrum which was generated from a reaction of molecular fluorine with dimethyl selenide. Figure 11 shows the spectrum. 

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