NMR Spectroscopy of Naturally Occurring Phloroglucinol Derivatives

Abstract

¹³C NMR spectra of a number of methyl and acyl substituted derivatives of phloroglucinol and its monomethyl ether were recorded and interpreted. The aromatic carbon signals were assigned on the basis of proton coupled spectra in acetone–d₆ and acetone–d₆/ D₂O solutions. The substituent effects of the methyl and O–methyl groups on the aromatic carbon chemical shifts were calculated. These appeared to vary from compound to compound presumably owing to varying steric effects between the substituents and the parameters are thus of limited use in assignment of the signals of these compounds. The steric interactions in the three methylbutyrylphloroglucinol monomethyl ethers were discussed in terms of their ¹³C NMR chemical shifts. A proof for the presence of the keto form of methylbutyrylphloroglucinol was found : addition of D₂O to its solution in acetone–d₆ caused a considerable reduction of intensity of the signal of the unsubstituted carbon and all long range Jen couplings to the proton at this position practically vanished.

Key Word Index

¹³C NMR Spectroscopy - Phloroglucinol Derivatives - Dryopteris - Hagenia - Mallotus