Carbonyls electronic spectra

Initiated by the pioneering work of Burawoy [51 ], a number of experimental and theoretical studies were performed on the carbonyl group [52-55]. A complete review is beyond the scope of this paper. We will mention only some of them that we consider of particular importance for a comprehensive coverage of the electronic spectrum of formaldehyde for both the theoretical and experimental points of view. 

Electronic Spectrum. Propynal exhibits a sharp, clearly structured absorption band with 382.1 nm as the 0-0 transition. This band has been studied extensively in absorption (38,39) and emission, and has been shown to be that of the iA" +- - -A transition. It is only recently, however, that optically excited emission has been observed. At longer wavelengths starting about 420 nm, a weak absorption band was observed. This is probably due to the A" - A transition (111). Analysis of the 382.1-nm band has shown that the A" (n,ir ) state differs from that of many other carbonyl compounds in that it is planar there is no evidence that a planar excited state is at a potential maximum. 

Fig. 20. Electronic spectrum of a rhenium(I) carbonyl complex (23) featuring an optical charge transfer transition at Xj =lW nm involving a coordinated quinone acceptor ligand (181).

Osn. Only the diamagnetic OsnOEP-carbonyl compound is known and yields a normal electronic spectrum [576 (1,200) 540 (12,000) 509 (8,000) 393 (155,000] [Rohbock (152a)]. 

FSM-16, which may be due to the dominant interaction of nanowires with the inner acidic surface of the FSM-16 pores. The adsorption of hydrogen for Pt nanowires was one or two-orders of magnitude smaller than that for nanoparticles. In the IR carbonyl adsorption spectrum, Pt nanowires gave a weak band at 2080 cm corresponding to journal carbonyls, which was shifted to higher frequency than in the Pt nanoparticles (2060 cm ). This shift may reflect the electron-deficiency of the Pt atoms or the dipole coupling of CO on Pt nanowires in mesopores. ... 

Charge Transfer States in Cr(CO)f,. The electronic spectrum of metal carbonyl compounds is usually dominated by charge transfer (MLCT) transitions from the metal 2d orbitals into the CO it orbitals. In the case of Cr(CO)g, the 12 CO tt orbitals are found in the molecular orbitals 9fi , 2t2u, 2t g, and 2t2g. The region 3.5-7 eV in its spectrum is therefore built from a broad range of charge transfer transitions [200], of which, however, only two transitions are both spin and symmetry... 

The pigment responsible for the pink colour of the stem base and mycelium of Suillus americanus, S. bovinus, and S. collinitus has been isolated and shown to be a dimer, bovilactone-4,4 (230), of boviqui-none-4 389). Bovilactone-4,4 showed complex carbonyl absorption in the infrared spectrum [v o(carbon tetrachloride) = 1795, 1760, 1730, 1645, 1620 cm" and absorption maxima at 275, 382 and 460 nm (log 8 4.06, 3.92 and 3.95, respectively) in the electronic spectrum. The structure (230) was derived by comparison with the model compound (231) ( bisnorbovilactone ) which was prepared by heating 2,5-dihydroxy-1,4-benzoquinone under reflux in ethyl acetate in the presence of acetylated polyamide 392). Applying the same procedure to boviquinone-4 (using toluene as solvent) afforded bovilactone-4,4 (230) which confirmed its structure. 

Workman, G.L. and Duncan, A.B.F. (1970) Electronic spectrum of carbonyl fluoride. Chem. Phys., 52, 3204-3209. Kubota, N. (2007) Propellants and Explosives, 2nd edn, Wiley-VCH Verlag GmbH, Weinheim, p. 491. 

Figure Bl.6.12 Ionization-energy spectrum of carbonyl sulphide obtained by dipole (e, 2e) spectroscopy [18], The incident-electron energy was 3.5 keV, the scattered incident electron was detected in the forward direction and the ejected (ionized) electron detected in coincidence at 54.7° (angular anisotropies cancel at this magic angle ). The energy of the two outgoing electrons was scaimed keeping the net energy loss fixed at 40 eV so that the spectrum is essentially identical to the 40 eV photoabsorption spectrum. Peaks are identified with ionization of valence electrons from the indicated molecular orbitals.

A comparison of the relative basicities of pyrrole, furan and thiophene may be made by comparing the pK values of their 2,5-di-t-butyl derivatives, which were found to be -1.01, —10.01 and —10.16, respectively. In each case protonation was shown by NMR to occur at position 2. The base-strengthening effect of alkyl substitution is clearly apparent by comparison of pyrrole and its alkyl derivatives, e.g. A-methylpyrrole has a pKa. for a-protonation of -2.9 and 2,3,4,5-tetramethylpyrrole has a pK of 4-3.7. In general, protonation of a-alkylpyrroles occurs at the a -position whereas /3-alkylpyrroles are protonated at the adjacent a-position. As expected, electron-withdrawing groups are base-weakening thus A-phenylpyrrole is reported to have a p/sTa of -5.8. The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

The choice of the desired CM-partner directly influences the choice of the catalyst [147], Comparing the GII and the HII catalysts shows that the latter has access to a much broader spectrum of cross-partners [148], It is possible to use electron deficient cross-partners like acroleine, perfluorinated olefins, acrylonitrile, or other o / -unsaturated carbonyls, whereas GII leads to no reaction or very low conversions due to side-reactions in these cases. 

Compound 37a showed the absence of an aldehydic proton and the singlet around 8.15 ppm was assigned to the ethylenic proton located p with respect to the electron-withdrawing cyano and ester groups. The benzofuranyl coumarins 38 exhibited the carbonyl-stretching band around 1690 cm in the IR spectra (Table 6). PMR data for 13 compounds are given in Table 2. The El mass spectrum of 36a showed a molecular ion peak at m/z 324 (41%). 

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