TIGER

Other Resources: 12 results
Molecular Models of Antioxidants and Radicals  William 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.
Free Radicals |
Natural Products
Biologically Active Exceptions to the Octet Rule  Ed Vitz
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Lewis Structures |
Free Radicals |
Vitamins
Interactive Molecular Orbitals  William F. Coleman
The majority of Introductory Chemistry texts provide students with an adequate introduction to the visual aspects of the molecular orbital model for homonuclear diatomic molecules. The treatment of heteronuclear diatomic and polyatomic molecules is less uniform. Heteronuclear diatomics, when mentioned, are invariably treated as being derived from homonuclear diatomics. While the atomic orbital energy level differences in heteronuclear diatomics is sometimes pictured, the consequences of those differences for the resultant molecular orbitals are rarely discussed. The discussion of polyatomic molecular orbitals in these texts is limited to showing that parallel p-orbitals produce delocalized pi molecular orbitals. The molecules typically mentioned in this context are benzene, nitrate ion and carbonate ion. However, It is rarely pointed out that the six p-orbitals in benzene would form 6 pi molecular orbitals, and that only one of these orbitals would look like the picture in the text.These interactive modules are designed to clarify this subject.
MO Theory
Exceptions to the Octet Rule  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Lewis Structures |
Free Radicals |
Molecular Properties / Structure
Molecular Orbitals  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
MO Theory |
Magnetic Properties
Delocalized Electrons  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Resonance Theory |
MO Theory
Hybrid Orbitals  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Molecular Properties / Structure |
MO Theory
Interactive Molecular Orbital Diagrams  William F. Coleman
Here is an application for constructing the molecular orbital electron configurations of heteronuclear diatomic molecules. Energy level diagrams are given for the two different cases encountered in heteronuclear diatomics of the first short period (Li2 - Ne2). This is a useful tool for having students explore questions of bond order, magnetic properties and numbers of unpaired electrons.
Covalent Bonding |
MO Theory |
Enrichment / Review Materials
Heteronuclear Diatomic Molecular Orbital Formation  William F. Coleman
Here is a set of movies that demonstrates heteronuclear diatomic molecular orbital formation. The orbitals start at a distance where there is little or no interatomic interaction and move to the appropriate bond distance. Orbital phase is shown by the different colors.
Covalent Bonding |
MO Theory |
Enrichment / Review Materials
Hückel Determinant Solver  Robert M. Hanson
Generates energy diagrams for simple Hückel molecular orbital systems using JavaScript. You can specify the determinant or select one for a specific compound from a list.
Computational Chemistry |
MO Theory |
Theoretical Chemistry |
Enrichment / Review Materials
Inorganic Molecules; A Visual Database  Charles E. Ophardt, Evan M. Davis, Dustin Underwood
Inorganic Molecules: A Visual Data Base contains text and graphics describing 66 molecules and ions commonly used as examples in general chemistry courses. For each molecule, fifteen molecular properties are presented visually by eight or nine different molecular models created by the CAChe Scientific Molecular Modeling program.
Atomic Properties / Structure |
MO Theory |
Molecular Properties / Structure
Restricted Hartree-Fock SCF Calculations Using Microsoft Excel  Mark A. Freitag, Cortney A. Boots, Taylor R. Page
Courses in computational chemistry are increasingly common at the undergraduate level. Excellent user-friendly programs, which make the execution of ab initio calculations quite simple, are available. However, there is a danger that the underlying SCF procedure (usually coupled with contracted Gaussian atomic orbital basis sets) can become a ?black box? for the student. This Microsoft Excel spreadsheet contains all the essential elements of far more complicated ab initio calculations, but on the simplest possible molecular system.
Computational Chemistry |
Mathematics / Symbolic Mathematics |
MO Theory |
Quantum Chemistry |
Theoretical Chemistry