Chemical Education Today
Book & Media Reviews The Molecular Modeling Workbook for Organic Chemistry Warren J. Hehre, Alan J. Shusterman, and Janet E. Nelson. Wavefunction, Inc.: Irvine, CA. 1998. 307 pp. ISBN 1890661-06-6. $30.00.
This workbook is the latest in a series of “lab manuals” designed to increase the presence of molecular modeling and computational chemistry in undergraduate courses. The authors have designed the workbook to differ from its predecessors in two ways: the target audience is introductory organic chemistry students, and a CD-ROM containing files of molecules and data replaces the need for expensive molecular modeling software. It also differs from its predecessors in that the exercises in it are not really molecular modeling experiments. Instead, students are introduced to the field by viewing the results of computational work stored on the CD-ROM. The workbook is divided into 21 chapters, each of which covers a topic encountered in introductory-level organic chemistry. The sequence of chapters follows the sequence of topics that instructors of introductory organic courses might employ, allowing the workbook to be used with most modern organic chemistry texts. The heart of the workbook, though, is the CD-ROM included with the book. It contains files of molecules and their accompanying computational results as well as Spartan View, a software package that allows these models to be visualized. Although it does not allow actual calculations to be performed, Spartan View permits the user to rotate molecules, intermediates, and transition states and retrieve “precalculated” values of bond and dihedral angles, bond lengths, energies, dipole moments, charge, and frequency of vibration. Spartan View also allows the user to search molecules and intermediates for electron-rich or electron-poor regions by showing electrostatic potential as well as HOMOs and LUMOs. Some files allow for animation of reactions or conformational changes. Note, however, that since the data are just stored on the CD-ROM, not all the data are available for all files. Although performing calculations is not an option, Spartan View can be used to display models and data obtained using Spartan or MacSpartan and stored on a disk. In this way, student exercises can be customized by the instructor or the instructor can prepare customized examples for use in lecture. Each chapter in the workbook contains a series of 3 to 17 exercises that use models and associated data contained on the accompanying CD-ROM. The exercises are not simply cookbook procedures in which the student is directed how to solve a problem. Instead, the authors provide background in a two-part tutorial and several essays that describe the information that can be obtained through molecular modeling, and then introduce a problem in organic chemistry that can be addressed using molecular modeling. The student is left to determine how best to obtain the requested data. For example, an exercise in the chapter Acids & Bases directs the student to determine the atomic charges and view the electrostatic potential map of the conjugate bases of three organic
acids. The student is not, however, told which menu to pull or button to push. At the end of the exercise, the student is directed to compare the reactivity of the acids with the data collected from Spartan View. The exercises are relatively easy to complete after spending a few minutes with the tutorials, and many require students to compare the results of calculations with the reactivity of the molecules as discussed in the traditional lecture portion of the course. In this sense, the workbook provides a meaningful link between molecular modeling exercises outside of class and activities in the classroom. While some exercises involve comparing the energies of intermediates or transition states, others are more like videos of processes. Instructors will find many of these to be useful as visual aids in lecture. Mechanisms of Ring Inversion, for example, allows the instructor to show the stepwise ring flip of cyclohexane. Although some of the animations are very similar to those contained on CD-ROMs that sometimes accompany textbooks, the exercises in this workbook allow for the retrieval of data such as the energies of the various conformations cyclohexane. Not only can the student see the stepwise conversion of one chair conformation into another, but the changes in energy as the ring flip occurs are available. Also, unlike many of the visualizations on the CD-ROMs packaged with textbooks, these give the student control over the orientation of the structures on the screen, allowing views from numerous angles. The possibility of the instructor’s customizing the exercises adds to the appeal of this workbook. In reviewing this book, I noted a couple of problems. The energy of molecules is presented in hartrees or atomic units (au). Although a factor is given for converting these values into the more familiar kcal/mol or kJ/mol, wouldn’t it be easier to use these results if they were given in the units that are more typically used in introductory organic chemistry texts? Similarly, a number of exercises ask the student to plot data that they have calculated in the exercise. However, no routine for plotting the data is included with Spartan View and students must go through the cumbersome process of copying the values and preparing the plots using another program or by hand. And, finally, in Tutorial B, animations are introduced by showing “the SN2 displacement of chloride in tert-butyl chloride by bromide.” Although the animation shows an SN1 mechanism with the C–Cl bond breaking before approach of the incoming bromide ion, students who are new to organic mechanisms will be misled by the erroneous description in the workbook. Although instructors may want to carefully consider whether to add an additional $30 to the already high cost of required texts, this workbook provides a unique and potentially valuable addition to the introductory organic chemistry course. With many exercises involving the visualization of electrostatic potentials and HOMOs and LUMOs, it adds an increased presence of physical organic chemistry in the introductory course. And, although the exercises are not really molecular modeling, this workbook also provides a lowcost introduction to the field without the considerable cost of modeling software. If Spartan or MacSpartan is already available in the department, the possible tie-in with the workbook and the capability to project the results should
JChemEd.chem.wisc.edu • Vol. 76 No. 9 September 1999 • Journal of Chemical Education
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Chemical Education Today
Book & Media Reviews make this an attractive addition to any instructor’s repertoire of visualization tools for lecture. The Molecular Modeling Workbook for Organic Chemistry is definitely worthy of consideration by anyone interested in adding molecular modeling to the organic course. R. David Crouch Department of Chemistry Dickinson College Carlisle, PA 17013-2896
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Journal of Chemical Education • Vol. 76 No. 9 September 1999 • JChemEd.chem.wisc.edu
