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Alkanes and Cycloalkanes The structures and conformations of alkanes and cycloalkanes and the vibrational, rotational, and translational motion of alkanes in the gas phase are demonstrated.
Alkanes / Cycloalkanes
Combustion of Methane Methane combustion in balloons, a Bunsen burner flame, and methane combustion in chlorine are demonstrated.
Alkanes / Cycloalkanes |
Reactions
Combustion of Hexane Combustion of hexane with limited oxygen and addition of water to burning hexane are demonstrated.
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.
Alkenes |
Free Radicals |
Green Chemistry |
Qualitative Analysis |
Reactions
Free Radical Halogenation, Selectivity, and Thermodynamics: The Polanyi Principle and Hammond's PostulateAlfred A. Scala Free radical halogenation reactions are examined in the contexts of the Polanyi principle and Hammond's postulate and used as a vehicle for examination of the concept of selectivity in chemical reactions. The origin of selectivity is related to the thermodynamics of the competing reactions and their chemical dynamics. Scala, Alfred A. J. Chem. Educ.2004, 81, 1661.
Free Radicals |
Molecular Mechanics / Dynamics |
Computational Chemistry |
Kinetics |
Thermodynamics
Application of Hammond's Postulate. An Activity for Guided Discovery Learning in Organic ChemistryJ. E. Meany, Vicky Minderhout, and Y. Pocker In this activity, students are given product distributions and other relevant experimental data concerning the free radical chlorination and bromination of propane. Students are guided in the use of Hammond's postulate to predict transition-state structures and to provide a rationale for the relationship between selectivity and reactivity in these and other reactions. Meany, J. E.; Minderhout, Vicky; Pocker, Y. J. Chem. Educ.2001, 78, 204.
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.
