The Relationship of Molecular Representations, Complexity, and Orientation to the Difficulty of Stereochemistry Problems

This study investigated how molecular structure representations affect the difficulty of stereochemistry problems. A stereochemistry test was administered to 102 organic chemistry students. The test included four 18-item subtests in which students were asked to assign an R or S configuration to a molecule. Each of the four subtests used a different type of molecular structure representation: two-dimensional drawings (Fischer or Haworth projections), three-dimensional drawings (dashed-wedged structures), computer animated ball-and-stick models, and physical ball-and-stick models. Within each subtest the complexity and orientation of the structures were also varied. To reduce the impact of prior knowledge of stereochemistry principles on the scores, the test contained a copy of the rules for assigning absolute configuration and an example of how to apply them. Subtest scores showed that the more abstract the representation, the lower the mean score. The scores decreased as follows: physical models computer models three-dimensional drawings two-dimensional drawings. As expected, the more complex structures were significantly more difficult than simpler ones. The orientation of the lowest-priority group also influenced performance. Highest scores were achieved when the lowest-priority group in a dashed-wedged structure or computer model was pointing toward the back or to the side, rather than upward or toward the front.