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  • 1
    Electronic Resource
    Electronic Resource
    14N nuclear quadrupole resonance study of phase transitions of 1M and 2Or polytypes of potassium hexacyanoferrate (III) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6047-6053 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 14N nuclear quadrupole resonance (NQR) frequencies were measured between 77–328 K for simple monoclinic (1M) and orthorhombic (2Or) polytypes of potassium hexacyanoferrate (III) (KFR). A reversible first order transition was found at 133 K for 1M and at 138 K for 2Or polytype. The transition was interpreted in terms of the coupling of a quasisoft rotatory mode with a temperature dependent tilt motion of the complex ion. An irreversible interpolytype transition produced by internal strains was observed in a sample formed by 1M and 2Or polytypes and repeatedly cycled between around 80–140 K and room temperature. Selective broadening of lines observed in only a pair of N atoms of each hexacyanoferrate ion was attributed to the occurrence of one dimensional disorder of neighboring K ions. The disorder disappeared after sample recrystallization. It was found that low crystallization rates produced only the 1M structure while high rates increased the occurrence of the 2Or over 1M polytype and even produced a third polytype. Annealing of KFR for two weeks at 160 °C produced minor changes in polytypic composition thus showing a high energy barrier for interpolytypic conversion. The results obtained in KFR are explained in terms of the theory of order–disorder structures in layered compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451520
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of chain length on nuclear quadrupole interaction of nitrogen-14 in aminated n-alkanes (1983)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 21 (1983), S. 46-49 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 14N nuclear quadrupole resonance (NQR) spectra of several aminated n-alkanes of the type CH3(CH2)xNH2(CH2)xNH2 at 77 K are reported and analysed in the framework of a semi-empirical theory. The NQR data presented oscillations for x〈6 and reached limiting values for x≥6. The results obtained are discussed in terms of inductive and conjugative effects, as well as the possible contributions of the hydrogen bond network presented in the solid state.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/omr.1270210112
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  • 3
    Electronic Resource
    Electronic Resource
    14N NQR study of the effect of protonation on the charge distribution of some N-methylated ureasResearch partially supported by the CONICIT of Venezuela, Grant S1-1241. (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 145-149 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 14N NQR frequencies measured at 77 K for the amine group of the 1:1 salts of nitric acid with methylurea and 1,3- and 1,1-dimethylurea and the phosphoric acid salt of 1,3-dimethylurea are reported. The analysis of the NQR data showed that the N loses population from its π orbital. The decrease in π population is partially compensated by an increase in the population of the N—C σ bonds. The loss of π population is enhanced when the H atoms of the amine group are substituted by electron-donating groups such as CH3.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230302
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