A nitrogen-15 NMR study of hydrogen bonding in 1-alkyl-4-imino-1,4-dihydro-3-quinolinecarboxylic acids and related compounds

✍ Scribed by Laurence Carlton; Benjamin Staskun; Theodorus van Es

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 122 KB
• Volume: 44
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1760

✦ Synopsis

Abstract

The title compounds contain groups (amine, amide, imine, carboxylic acid) that are capable of forming intramolecular hydrogen bonds involving a six‐membered ring. In compounds where the two interacting functional groups are imine and carboxylic acid, the imine is protonated to give a zwitterion; where the two groups are imine and amide, the amide remains intact and forms a hydrogen bond to the imine nitrogen. The former is confirmed by the iminium ^15^N signal, which shows the coupling of ^1^J(^15^N,^1^H) −85 to −86.8 Hz and ^3^J(^1^H,^1^H) 3.7–4.2 Hz between the iminium proton and the methine proton of a cyclopropyl substituent on the iminium nitrogen. Hydrogen bonding of the amide is confirmed by its high ^1^H chemical shift and by coupling of the amide hydrogen to (amide) nitrogen [(^1^J(^15^N,^1^H) −84.7 to −90.7 Hz)] and to ortho carbons of a phenyl substituent. Data obtained from N,N‐dimethylanthranilic acid show ^15^N^1^H coupling of (−)8.2 Hz at 223 K (increasing to (−)5.3 Hz at 243 K) consistent with the presence of a N··· HO hydrogen bond. Copyright © 2006 John Wiley & Sons, Ltd.