An essential skill for chemists is analyzing evidence to determine the outcome of the reaction. In this experiment, students react p-benzoquinone with cyclopentadiene. The visible absorbance of the reaction at several wavelengths is observed using a Microlab measurement system. The absorbance at 430 nm and 470 nm decreases. The absorbance at 383 nm and 400 nm initially increases, and then decreases. Students are primed with the relationship between the extent of conjugation and the UV-visible wavelength of absorption and with the Beer–Lambert Law. The students are then asked to use a qualitative understanding of the relationship between concentration and absorbance, combined with the conjugation/wavelength relationship, to determine what reactions are occurring. Students are capable of determining that there are two successive Diels–Alder reactions, the second of which is much slower than the first.
Jonathan Rhoad (Thu,) studied this question.