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  • 1
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1430-4171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A convenient inorganic laboratory exercise is presented that exposes the student to the influences of ligand substituents on a metal center’s redox properties. Students prepare a series of compounds with the general formula [Ru(bpy)2(R1,R2mal)](PF6), where bpy is 2,2′-bipyridine and R1,R2mal is an anionic β-diketone ligand with various R1 and R2 substituents. Each complex is prepared in a single synthetic step, and the Ru(III)/Ru(II) couple is characterized by cyclic voltammetry. The potential of the Ru(III)/Ru(II) couple shifts upon varying R1 and R2 from 0.64 to 1.10 volts vs. SSCE in the following order: (R1 = R2 = Me) 〈 (R1 = R2 = Ph) 〈 (R1 = Me, R2 = CF3) 〈 (R1 = R2 = CF3). The inductive effects of the R substituents on the Ru(III)/Ru(II) couple are consistent with their electron-donating and electron-withdrawing properties. Hammett constants for the substituents provide an approximate measure of these effects. A linear relationship is observed when the Hammett constants are plotted against the Ru(III)/Ru(II) potential. This laboratory exercise applies a versatile electroanalytical method, cyclic voltammetry, to measure the substituent effects on a metal center’s electron density. Student results of the syntheses and redox characterizations of a series of [Ru(bpy)2(R1,R2mal)]+ complexes are presented and discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1430-4171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An environmentally friendly redox laboratory for the determination of Fe(II) in an acid aqueous medium is presented. This laboratory exercise is an appropriate substitute for the traditional dichromate titration, which is environmentally problematic. This titration method uses the periodate ion as the oxidizing agent and yields results which are as accurate as the dichromate titration. Student success rate in quantitative analysis is better than 80% in two separate laboratory-based trials. This method requires a fairly high degree of operator skill to yield good results, making this a viable laboratory exercise at the sophomore or junior level.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1430-4171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Polarity of molecules is one of the central concepts that is used for predicting or rationalizing a wide array of concepts in the undergraduate chemistry curriculum. These concepts include the physical properties of molecules at the freshman level, structure-reactivity relationships in organic and inorganic chemistry, and selection rules in spectroscopy. In all of the freshman chemistry textbooks that we examined, bond dipoles are assigned based on electronegativity differences, which are then added vectorially (sometimes implicitly) to obtain the net dipole moment for a given molecule. We have found that this approach, which relies on the students’ familiarity and comfort level with vector addition in three dimensions, works well only for a small fraction of our students. We present an alternative pedagogical method for conveying this important concept. This method does not invoke vector addition, relying instead on a simple, pictorial approach that is transparent to a majority of our students. This method applies not only to species with a clearly defined central atom but to substituted alkenes and substituted benzenes as well. In addition, it can also be extended to paramagnetic species, whose polarity is not generally discussed in most freshman chemistry textbooks.
    Type of Medium: Electronic Resource
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