NMR studies of intramolecular proton exchange in alkylated naphthazarins

✍ Scribed by Gülnur A. Elöve; J. Herman Schauble

• Book ID: 102951282
• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 596 KB
• Volume: 25
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260250303

✦ Synopsis

Three groups of alkyl-substituted naphthazarins were studied by 'H and "C NMR in chloroform-d at ambient temperature. Preliminary 'H NMR studies were carried out on selected members of each group at low temperatures (down to -120 "C) in dichloromethaue-d, solution. Monoalkylnaphthazarins were found to exist predominantly as the 2-alkyl tautomers ( I ) and the dimethylalkyl species as the 2,3-dimethyl-6-alkyl tautomers (I). However, both symmetrically and unsymmetrically substituted 2,6-and 2,7-dialkylnaphthazarins exhibited averaged chemical shifts and coupling constants indicating rapid proton exchange between the two minimum energy 174-dione tautomers ( I and ZZ). I3C NMR shifts were utilized to calculate tautomer populations of the unsymmetrical 2,6-and 2,7-(methyl, a1kyl)naphthazarins.