A graduate student was following a procedure to make 3-propylcyclohexa-1,4-diene. During the workup procedure, his research adviser called him into her office. By the time the student returned to his bench, the product had warmed to a higher temperature than recommended. He isolated the product, which gave the appropriate = C - H stretch in the IR, but the C = C stretch appeared around 1630 cm-1 as opposed to the literature value of 1650 cm-1 for the desired product. The mass spectrum showed the correct molecular weight, but the base peak was at rather than at M - 43 as expected. Because of the anomalous IR spectrum, he took a UV spectrum that showed max λmax at 261 nm.
(a) Should he have his IR recalibrated or should he repeat the experiment, watching the temperature more carefully? What does the 1630 cm-1 absorption suggest?
(b) Draw the structure of the desired product, and propose a structure for the actual product.
(c) Show why he expected the MS base peak to be at M-43, and show how your proposed structure would give an intense peak at M-29.