The assignment of 1H and 13C chemical shifts for dihydro-3(2H)-furanone derivatives by means of specific 2H labelling experiments and 13C{1H} decoupling experiments

• Published in: Canadian journal of chemistry Vol. 54; no. 9; pp. 1449 - 1453
• Main Authors: Burke, Patrick M, Reynolds, William F, Tam, Janet C. L, Yates, Peter
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.05.1976
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v76-208

The 1 H nmr spectrum of dihydro-2,2,5,5-tetramethyl-3(2H)-furanone ( 1 ) in 80% sulfuric acid shows a time-dependent decrease in the intensity of the lower-field gem-dimethyl signal relative to the upper-field gem-dimethyl signal. This is interpreted as involving reversible opening of 1 to 2-hydroxy-2,5-dimethyl-4-hexen-3-one, resulting in deuterium exchange at the C-5 methyl groups of 1 . The lower-field gem-dimethyl signal of 1 in this medium is therefore assigned to these methyl groups. A similar relationship between the methyl proton signals of 1 in organic solvents has been demonstrated by (i) synthesis of 1 -d 8 ( 8 ), (ii) comparison of the 1 H nmr spectra of 1 and its 2,2- and 5,5-dimethyl analogs, and (iii) observation of long range coupling in the spectrum of 1 . Assignment of 13 C chemical shifts for 1 has been made based on protoncoupled spectra, showing that the signal of the C-5 methyl carbons appears at ca. 4 ppm towards lower field than that of the C-2 methyl carbons. Both the 1 H and 13 C chemical shift assignments for 1 were confirmed from 13 C{ 1 H} spectra using low power single frequency 1 H decoupling, demonstrating the utility of this technique for the assignment of chemical shifts.