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Blue Bottle, Red and Blue Bottle Color changes are caused by reactions of oxygen in the air with chemicals in a solution. The colors fade over time, but can be regenerated by shaking the flask containing the solution.
Kinetics |
Mechanisms of Reactions |
Oxidation / Reduction
Induction by Iron(II) of the Oxidation of Iodide by Dichromate Acidic aqueous solutions containing dichromate and iodide ions are mixed with no reaction. The addition of a solution of iron(II) ion induces the rapid formation of brown triiodide ion.
Teaching a Modified Hendrickson, Cram, and Hammond Curriculum in Organic ChemistryJoel M. Karty, Gene Gooch, and B. Gray Bowman Describes a new organic chemistry curriculum in which fundamental concepts are introduced before mechanisms, and mechanisms are introduced before reactions. Reactions are introduced according to similarities among mechanisms rather than the functional group involved. Karty, Joel M.; Gooch, Gene; Bowman, B. Gray. J. Chem. Educ.2007, 84, 1209.
Learning Theories |
Mechanisms of Reactions
"You're Repulsive!"Teaching VSEPR in a Not-So-Elegant WayRobert S. H. Liu Valence shell electron pair repulsive (VSEPR) interaction is an important concept particularly in discussing structural properties of molecules. In this article we showed five organic examples not commonly associated with VSEPR but yet all involving repulsive interactions of valence electrons, which provides ready explanations for altered chemical reactivity and spectroscopic properties of organic compounds. The ready catchy phrase Youre Repulsive! is the common thread used throughout these five examples. Liu, Robert S. H. J. Chem. Educ.2005, 82, 558.
Mechanisms of Reactions |
UV-Vis Spectroscopy |
Reactions |
Addition Reactions |
Electrophilic Substitution
A Substitute for “Bromine in Carbon Tetrachloride”Joshua M. Daley and Robert G. Landolt Benzotrifluoride (BTF) is a suitable solvent substitute for carbon tetrachloride in experiments requiring application of bromine (Br2) in free radical or addition reactions with organic substrates. A 1 M solution of Br2 in BTF may be used to distinguish hydrocarbons based on the ease of abstraction of hydrogen atoms in thermally or light-induced free radical substitutions. Efficacy of minimization of solvent use, by aliquot addition to neat samples, has been established. Daley, Joshua M.; Landolt, Robert G. J. Chem. Educ.2005, 82, 120.
Molecular Models of Antioxidants and RadicalsWilliam F. Coleman This month's featured molecules come from the paper by John M. Berger, Roshniben J. Rana, Hira Javeed, Iqra Javeed, and Sandi L. Schulien (1) describing the use of DPPH to measure antioxidant activity. DPPH was one of the featured molecules in September 2007 (2) and the basics of antioxidant activity were introduced in last month's column (3). In addition, some of the other molecules in the paper are already in the featured molecules collection (4). The remaining structures in the Figure 1 and Table 1 of the paper have been added to the collection. All structures have been optimized at the 6-311G(D,P) level. These molecules suggest a number of possible student activities, some reminiscent of previous columns and some new. (R,R,R)-α-tocopherol is one of the molecules in the mixture that goes by the name vitamin E. These molecules differ in the substituents on the benzene ring and on whether or not there are alternating double bonds in the phytyl tail. In (R,R,R)-α-tocopherol the R's refer to the three chiral carbon atoms in tail while α refers to the substituents on the ring. (R,R,R)-α-Tocopherol is the form found in nature. An interesting literature problem would be to have students learn more about the vitamin E mixture and the differing antioxidant activity of the various constituents. Additionally they could be asked to explore the difference between the word natural as used by a chemist, and "natural" as used on vitamin E supplements. Can students find regulations governing the use of the term "natural"? Can they suggest alternative legislation, and defend their ideas? If students read about vitamin C they will discover that only L-ascorbic acid is useful in the body. It would be interesting to extend the experiment described in the Berger et al. paper (1) to include D-ascorbic acid. How do the antioxidant abilities of the enantiomers, as determined by reaction with DPPH compare? Is this consistent with the behavior in the body? Why or why not? Berger et al. mention two other stable neutral radicals, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and Fremy's salt. In a reversal from the use of stable radicals to measure antioxidant properties, these two molecules have proven to be very versatile oxidation catalysts in organic synthesis, and would make a rich source of research papers for students in undergraduate organic courses.
