The differences in the types of representations constructed during successful and unsuccessful problem-solving episodes were investigated within the context of graduate students working on problems that involve concepts from 2D-NMR. Success at problem solving was established by having the participants solve five problems relating to material just encountered within a computer-based tutorial. The results indicate that representations constructed during successful problem-solving episodes tend to be more accurate and more complete, but not as abstract as those constructed during unsuccessful problem-solving episodes. When more than a single representation was constructed, however, the additional representations associated with successful problem solving tended to be more abstract than those constructed during unsuccessful problem solving. The authors contend that the constructs of accuracy, abstractness, and completeness are useful for characterizing the differences in the representations constructed during successful and unsuccessful problem-solving episodes, and may serve as useful indicators of the degree of conceptual understanding the individual brings to the problem-solving event. (Contains 4 tables and 3 figures.)