Compound A exists in equilibrium with its tautomeric form, compound B. An IR spectrum of

Chapter 15, Problem 15.72

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Compound A exists in equilibrium with its tautomeric form, compound B. An IR spectrum of a mixture of A and B exhibits four signals in the region 1600-1850 cm-1 . These signals appear at 1620, 1660, 1720, and 1740 cm-1 (J. Am. Chem. Soc. 1952, 74, 40704073). O OH O A B C OEt O OEt O O OEt O EtO (a) Identify the source for each of these four signals and provide a justification for the location of the signal at 1660 cm-1 . (b) For most simple ketones, the concentration of the enol tautomer is almost negligible at equilibrium. However, in this case, the concentration of B is significant. Provide a justification for this observation. (c) The IR spectrum of compound C lacks a signal at 1720 cm-1 . Draw the tautomer of C and then determine which tautomeric form predominates at equilibrium. Explain your choice.