The Crystal and 3-Dimensional Molecular Structures of Compounds as Determined by X-Ray Diffraction
Project Description
Knowledge of the 3-D structure of a molecule frequently leads to a deeper understanding of its reactivity. Since models (kits or VSEPR methods) typically provide somewhat approximate (~ 2 significant figures) geometrical information (i.e., distances and angles), a superior method is needed to better understand molecular behavior.
X-ray diffraction (XRD) is one such method. As an example, consider how Watson and Crick's discovery of the structure of DNA has had a profound impact on the field of molecular biology. XRD relies on the ability of crystalline material to diffract X-rays. Consequently, analyses can only be performed on very pure crystalline samples. Fortunately, the sample size requirement is very small (~0.3-0.5 mm on an edge, which corresponds to the size of a printed period!). For a typical organic compound, this translates to 30-150 μg.
Once a "good" crystal is available, data collection, typically taking 2-7 days, is performed. Afterwards, extensive computer analyses nearly always result in a set of very precise atomic coordinates. From these coordinates distances and angles can easily be calculated to 4 significant figures, and a computer-generated representation ("picture") of the molecule as it exists in the crystal can be produced. Example pictures are on Truman's Chemistry (Dr. Baughman's) web site (http://chem.truman.edu). As another indication of the importance of the information, it can often be the basis for a publication in a peer-reviewed journal.
Truman is one of 7 institutions in Missouri, and the only solely undergraduate program, with the necessary instrument and software to accomplish crystal analyses. Current work (i.e., projects already available) in the Truman State University diffraction laboratory includes determinations of the 3-D structures of various pesticides, charge-transfer complexes, and numerous other compounds (e.g., lead complexes, porphyrins) in collaboration with Truman and other university research labs.
Although mainstreaming into existing projects is one option, analysis of crystals generated in other undergraduate research and/or community college faculty projects could certainly be considered for the summer research. Dr. Baughman would be happy to discuss current and future projects.
X-ray diffraction (XRD) is one such method. As an example, consider how Watson and Crick's discovery of the structure of DNA has had a profound impact on the field of molecular biology. XRD relies on the ability of crystalline material to diffract X-rays. Consequently, analyses can only be performed on very pure crystalline samples. Fortunately, the sample size requirement is very small (~0.3-0.5 mm on an edge, which corresponds to the size of a printed period!). For a typical organic compound, this translates to 30-150 μg.
Once a "good" crystal is available, data collection, typically taking 2-7 days, is performed. Afterwards, extensive computer analyses nearly always result in a set of very precise atomic coordinates. From these coordinates distances and angles can easily be calculated to 4 significant figures, and a computer-generated representation ("picture") of the molecule as it exists in the crystal can be produced. Example pictures are on Truman's Chemistry (Dr. Baughman's) web site (http://chem.truman.edu). As another indication of the importance of the information, it can often be the basis for a publication in a peer-reviewed journal.
Truman is one of 7 institutions in Missouri, and the only solely undergraduate program, with the necessary instrument and software to accomplish crystal analyses. Current work (i.e., projects already available) in the Truman State University diffraction laboratory includes determinations of the 3-D structures of various pesticides, charge-transfer complexes, and numerous other compounds (e.g., lead complexes, porphyrins) in collaboration with Truman and other university research labs.
Although mainstreaming into existing projects is one option, analysis of crystals generated in other undergraduate research and/or community college faculty projects could certainly be considered for the summer research. Dr. Baughman would be happy to discuss current and future projects.
Background Needed
Knowledge of basic solid state ideas (unit cell, Bragg equation, waves) as well as familiarity with Windows and DOS operating systems is needed. If one has questions please feel free to contact Dr. Baughman.