An organic chemist isolates an unknown compound, C₉H₁₀O₂
CHEMISTRY · Multi-part · A Level · Chemistry · Organic analysis and spectroscopy · Organic analysis and spectroscopy
Problem
An organic chemist isolates an unknown compound, C₉H₁₀O₂, suspected to be either an ester or a conjugated ketone. The laboratory has unrestricted access to microwave, IR, and UV-Vis spectrometers, but the chemist wants to minimize instrument time by selecting only the two most informative techniques.
Answer the following.
(a) Propose a sequence of two spectroscopic analyses that will allow the chemist to (i) determine whether the compound contains a carbonyl functional group and (ii) assess whether the π-system is conjugated. State clearly which technique is performed first and which is performed second.
(b) For each technique in your sequence, explain the specific molecular transition it probes and describe the diagnostic spectral evidence that would differentiate between an ester and a conjugated ketone.
(c) Suppose the IR spectrum acquired in part (a) shows a sharp absorption at 1 730 cm⁻¹ and no significant peaks between 1 600 and 1 650 cm⁻¹. Predict the most likely functional class of the compound and justify your prediction using both the observed IR data and the expected outcome of the second technique in your sequence.
(d) If instrument access were unlimited, explain how adding the third spectroscopic technique could provide complementary structural information not obtainable from the first two.