Refine
Year of publication
Document Type
- Article (40)
Language
- German (40) (remove)
Has Fulltext
- yes (40)
Is part of the Bibliography
- no (40) (remove)
Keywords
- PE Spectra (7)
- ESR Spectra (5)
- ESR/ENDOR Spectra (5)
- MNDO Calculations (5)
- Cyclic Voltammetry (4)
- Single Crystal Structure (4)
- Single Crystal Structures (4)
- Contact Ion Pairs (3)
- Crystal Structure (3)
- Cyclovoltammetry (3)
Institute
- Biochemie und Chemie (40) (remove)
Photoelektronen-Spektren und Moleküleigenschaften, 110 [1,2]. Tricyanmethan-Derivate X—C(CN)3
(1987)
The photoelectron spectra of tricyanomethane derivatives X-C(CN)3 with substituents X = H, CH3, Br and C6H5 have been recorded and are assigned based on MNDO calculations as well as on radical cation state comparison with the iso(valence)electronic P(CN)3, within the series of cyanomethanes H4-nC(CN)n, and with each other. For HC(CN)3, no traces of the isomeric dicyano, ketimine HN = C=C(CN)2 are detected in the gas phase. Tricyanomethylbenzene, H5C6-C(CN)3, exhibiting the highest first ionization energy of any known singly acceptor substituted phenyl derivative, demonstrates the tremendous electron withdrawing effect of the -C(CN)3 group.
The HCl elimination from β-chloroethyl azide (1-azido-2-chloroethane) over potassium tert. butanolate at 350 K in a low pressure flow system is optimized using PE spectroscopic real-time gas analysis. The highly explosive vinyl azide formed can be purified by cool-trapping the by-products. Its subsequent and virtually hazard-free pyrolysis yields 2H-azirine, which can be isolated at temperatures below 240 K.
In contrast, the direct pyrolysis of β-chloroethyl azide requires temperatures above 710 K and results in a simultaneous split-off of both HCl and N2, yielding acetonitrile as the main thermolysis product. No intermediates such as β-chloroethanimine or ketenimine are observed, a result which is interpreted in terms of chemical activation.
Trifluoromethyl azide decomposes in a low-pressure flow system at rather high temperatures by splitting off N2. The nature of the resulting products depends largely on the wall material of the pyrolysis tube: using molybdenum above 1120 K, FCN is observed exclusively. Neither F2C=NF nor F3C-N=N-CF3 can be detected as intermediates by comparing their PE spectra with those continuously recorded while increasing the temperature. F3C-N = N - CF3 fragments already at 870 K to give N2 and F3C-CF3. The PE spectra of F3CN3 and F2C=NF are assigned based on MNDO calculations.
The reactive intermediate methyleneaminoacetonitrile H2C = N - C H2 - CN has been generated via thermal retrotrimerization of N ,N',N"-tris(cyanomethyl)hexahydro-s-triazine and characterized by its photoelectron, mass and low-temperature NMR spectra. A fully geometryoptimized MNDO calculation allows to assign the observed ionization energies and yields estimates for other molecular properties, e.g. a rather high dipole moment.
For the first time, 107,109Ag ENDOR measurements in solution are reported. In addition, the formation of the known paramagnetic contact ion pair [Ag⊕(PR3)2(R2H2C6O2·⊖] on reduction of 3,5-di(tert-butyl)-o-benzoquinone in THF solution containing soluble silver salts and triphenylphosphine is studied by cyclic voltammetry.
Di(methylthio)acetylene H3CS-C≡C-SCH3 reacts with S2C12 in AlCl3/H2CCl2 solution to the tetra(thiomethyl)thiophene radical cation (H3CS)4C4S·⊕ and with H3CSCl to the tetra(thiomethyl)ethene radical cation (H3CS)2C·=⊕C(SCH3)3. Their ESR spectra are assigned by comparison with literature data or those of analogous products obtained from other acetylene derivatives R-C≡C-R with R = SCH2CH3, CH3, C6H5 as well as based on HMO arguments. The possible course of the oxidative sulfuration is discussed.
The structurally different radical anions M⊖ of peralkylated 1-sila-2,5-diazacyclopentane-3,4-dithione and of tetrakis(isopropylthio)-p-benzoquinone are generated by reduction with potassium/2.2.2-cryptand under aprotic conditions in THF solution. On addition of Li⊕B(C6H5)4⊖, both form hitherto elusive sulfur-containing contact ion pairs, which are characterized by their ESR/ENDOR spectra.
Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties. Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K. Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or 1-bromopropene-2. HCl elimination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene. Most interesting, however, is the ring opening of monobromo cyclobutane to 1-bromo-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chemisorbed surface carbene at Raney nickel. The formation of hexadiene-1,5 as a by-product in the HCl elimination of 1-chloropropane, i. e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.
Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties. Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K. Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or l-brom opropene-2. HCl elim ination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene. Most interesting, how ever, is the ring opening of monobromo cyclobutane to 1-brom o-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chem isorbed surface carbene at Raney nickel. The formation of hexadiene-1,5 as a by-product in the HCl elim ination of 1-chloropropane, i.e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.
Conditions for ENDOR measurem ents of organosulfur radical cations are discussed and tested. The one electron oxidation of a variety of aromatic sulfur com pounds comprising benzene-1,2-dithiole, 1,4-dithiine, thianthrene and diphenylsulfide derivatives as well as 33S isotope-marked bis(2,5-dimethoxyphenyl)disulfide is accomplished using the oxygen-free, powerful and selective AlCl3/H2CCl2 reagent. Partly with substantial structural changes, paramagnetic M⊕ species of 1,2-benzodithiete, 1,4-dithiine, thianthrene and diphenyl sulfide result. Their temperature-dependent ENDOR signal patterns provide numerous information e.g. on radical cation structure and dynamics, on the rather high sulfur spin populations or on the spin rotation interaction dominated relaxation behaviour. Accordingly, to obtain optimum ENDOR effects in organosulfur radical cations low temperature measurements are required, and especially for still undiscovered 33S ENDOR couplings, small g factor anisotropies and 33S spin densities appear to be necessary.
The radical anion of dimesityltetraketone (ERed, I = -0.40 V) is easily generated in THF by potassium mirror/[2.2.2]-cryptand reduction. Its contact ion pairs with Na⊕, Cs⊕ and Ba⊕⊕ counter cations, prepared in THF solution by single electron transfer from the respective metals, are characterized by their ESR/ENDOR spectra, which exhibit temperature-dependent metal couplings of aNa⊕ = 0.061 mT (190 K), aCs⊕ = 0.021 mT (190 K), and aBa⊕⊕ = 0.145 mT (295 K).