Tautomerism and1H and13C NMR assignment of methyl derivatives of 9-hydroxyphenalenone

Abstract

9-Hydroxyphenalenone is a planar multicyclic beta-keto-enol that demonstrates C2V symmetry on the NMR timescale. Off-axis substitution breaks the molecular symmetry and results in tautomers. 1H and 13C NMR assignments were made for 9-hydroxyphenalenone and three methyl derivatives, and the solution-phase tautomers were determined.

Synthesis and Characterization of 9-Hydroxyphenalenone Using 2D NMR Techniques

“…1 The literature has few examples of synthesis experiments that utilize 2D experiments for characterization (8)(9)(10)(11)(12). 9-Hydroxyphenalenone is a planar multicyclic β-ketoenol, which results in equivalent tautomers and demonstrates C 2ν symmetry on the NMR time scale as shown in Figure 1A ( [14][15][16]. This unique structure has two distinct spin systems in the aromatic region, adequate spacing of the carbon signals, and a strongly deshielded hydroxyl proton at 16 ppm.…”