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  • 1
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational assignments for the skeletal modes of some complexes containing CH3SX2+ and (CH3)2SX+ (X = Cl, Br) have been made on the basis of their solid-state Raman spectra and compared with any previous data. The stabilities of the parent CH3SX3 and (CH3)2SX2 compounds are discussed; two isomers of (CH3)2SBr2 were obtained under varying reaction conditions and assigned as ionic [(CH3)2SBr+Br-] and charge-transfer [(CH3)2S → Br2] forms. The transition of the ionic (metastable) form to the more stable charge-transfer form was monitored by differential scanning calorimetry. High-frequency shifts occur in some fundamental modes of (CH3)2SBr+Br- when Br- is replaced with a polyatomic anion, analogous to those seen in halophosphonium complexes; this is rationalized in terms of anion-cation interaction.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational assignments for the skeletal modes of the solid-state species (CH3)nPX5-n (X = Cl, Br; 1 ≤ n ≤ 3) have been made on the basis of their Raman Spectra. The results are consistent with ionic formulations (CH3)nPX4-n +X- and are compared with any previously available data. Two modifications of (CH3)2PCl2 +Cl- have been observed for the first time and their relative stabilities investigated. Raman spectra of the mixed halogen cationic compounds CH3PCl2Br+X-, CH3PClBr2 +X- and (CH3)2PClBr +X- are also reported and Lewis acid complexes of all the phosphonium cations show characteristic high-frequency shifts in the P—X stretching modes [relative to those in (CH3) RPX4-n +X-] which are rationalized in terms of anion-cation interactions. CH3PCl4 has been observed in a molecular form and the transition to the ionic modification (at ca 160 K) has been monitored by variable temperature Raman spectroscopy.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectra of aqueous solutions of calf thymus histone complexes H2A:H2B and H3:H4 have been recorded and are compared with those of the individual histones. The results show an increase of α-helix content on formation of these complexes, at the expense of random-coil conformation in H2A:H2B and β-sheet structure in H3:H4. The α-helix content is estimated to be 40% in H2A:H2B and 35% in the H3:H4 complex. The intensity ratios of the 850/830 cm-1 components of the tyrosine doublet in the spectra of both complexes are the averages of the values for the individual histones, suggesting that the environment of these residues is little modified on formation of the complexes. Variations in the intensity of the 1400 cm-1 carboxyl band has been observed to be associated with conformational changes, which is consistent with the notion that COO-/NH3+, NH2+ interactions play a major role in histone-histone complexation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Syntheses of stable and metastable isomers for each of the chlorophenylphosphoranes, PhPCl4, Ph2PCl3 and Ph3PCl2, together with some Lewis acid salts are described. Comparison of Raman spectra of the salts with one set of isomers suggests an ionic formulation [PhnPCl4 - n+] [Cl-] (1 ≤ n ≤ 3); correlation with spectra of Sb and As analogues of known structure suggest pseudo-trigonal bipyramidal (Ψtbp) structures for the other isomers. Thermodynamically stable isomers are ionic Ph3PCl+Cl-, Ψtbp Ph2PCl3 and Ψtbp PhPCl4. Vibrational Raman assignments for the skeletal modes are given for each of the isomers and some of their Lewis acid salts. Frequency shifts arising from non-bonded interactions in the ionic species are compared with those in the methyl-substituted analogues.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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