Historically, isomerism-based chemistry topics have been observed to be difficult for students. Despite this anecdotal history, there is little quantitative evidence to support this claim; however, there have been studies that indicate that visual-spatial skills can be important for identification of spatial relationships required for isomerism topics.  Using an Item Analysis procedure, we have compiled quantitative evidence that indicates that isomerism-based questions qualified as moderately difficult based on the difficulty score for undergraduate chemistry students on multiple-choice exams. Difficulty scores between 0.3 and 0.8 are categorized as moderately difficult; this measure is independent of the overall exam difficulty.  Difficulty scores were calculated for an Introductory Organic Chemistry course that taught a varied population of students, including first year and upper-level students from a range of STEM and nursing majors and with different prerequisite course experience.  27 isomerism questions from 8 exams over 4 academic quarters were identified with 52% having moderate difficulty. Questions requiring the identification of structural isomers, 5 in total, were among the lowest difficulty scores on the exams when compared to the difficulty scores of all questions on the exam.  Further analysis indicated that previous coursework had an influence on student performance. Once the population was subdivided based on prerequisite coursework, difficulty scores were recalculated for each question for each population.  The scores for the isomerism questions for the population of students who had bypassed the General Chemistry sequence via AP test scores were consistently the highest. Additional analysis indicated that there was no difference in student performance on isomerism questions as a function of gender.

Quantitative investigation of non-chemistry majors’ difficulties with isomerism using item analysis

ACS Spring Meeting 2021

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