The 13C, H coupling constants in structural and conformational analysis. III.. Long-range carbon–hydroxyl proton couplings as evidence of hydrogen bonding in some acylphloroglucinols

✍ Scribed by Pertti Äyräs; Carl-Johan Widén

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 367 KB
• Volume: 11
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270111105

✦ Synopsis

Abstract

Proton coupled ^13^C NMR spectra have been recorded for some acylphloroglucinol derivatives. Significant couplings over two, three and four bonds were observed between the hydroxyl proton and aromatic carbons for those compounds where the hydroxyl group is hydrogen bonded strongly enough to the carbonyl carbon of the acyl side chain. Typical values were ^2^J = 4.8 Hz, and ^3^J = 5.6 Hz or 6.7 Hz corresponding to dihedral angles of c. 0° and c. 180°, respectively; the dihedral angle is defined as the angle between the O—H bond and the plane of the aromatic ring. A stereospecific ^4^J(COH) value of 1.2 Hz for a ‘W’ arrangement of coupled atoms was also found. An interesting example of ‘virtual’ J(CH) coupling was observed in the proton coupled spectrum of 1‐butyrylphloroglucinol 2‐monomethyl ether in acetone‐d~6~ caused by the accidentally equal chemical shifts of the two ring protons.