Computational Chemistry Experiments for an Organic Chemistry Course

This article, the second in a series of publications detailing computational experiments for use in an undergraduate curriculum, describes four exercises that can be incorporated into an Organic Chemistry Laboratory course. In the first experiment, students use computational chemistry to examine the conformations of alkanes and cycloalkanes. The students find the energy of each conformer, calculate the relative amounts of each conformer and discover that molecules do spend time in non-optimal conformations. To further explore why one conformer is preferred over another, students measure bond angles and the bond distances between hydrogen atoms on different carbon groups. In the second experiment, students examine alkene stability by calculating the energy of four isomers of C4H8 to study the effect of having alkyl groups adjacent to the double bond. They also look at the susceptibility of alkenes to electrophilic addition by plotting the electrostatic potential to determine which carbon atom of a double bond is more susceptible to electrophilic attack. The relative reaction rates can be found by calculating the energy difference between the reactants and the carbocation intermediates. This experiment is the first time that students build and perform calculations on ionic species. Experiments 3 and 4 are paired exercises showing how different benzene ring substituents affect the susceptibility of the ortho, meta, and para positions to either electrophilic or nucleophilic aromatic attack. These experiments compliment what students learn in class, as well as expose them to some of the information that can be acquired using computational chemistry. These four experiments can be incorporated into the organic chemistry sequence, either as a group or individually, depending on the needs of the department and the student population.