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

Laurence Carlton*, Benjamin Staskun, Theodorus Van Es

*Corresponding author for this work

Research output: Contribution to journalArticle

5 Citations (Scopus)

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 15N signal, which shows the coupling of 1J( 15N,1H) -85 to -86.8 Hz and 3J( 1H,1H) 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 1H chemical shift and by coupling of the amide hydrogen to (amide) nitrogen [(1J( 15N, 1H) -84.7 to -90.7 Hz)] and to ortho carbons of a phenyl substituent. Data obtained from N,N-dimethylanthranilic acid show 13N-1H 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.

Original languageEnglish
Pages (from-to)510-514
Number of pages5
JournalMagnetic Resonance in Chemistry
Volume44
Issue number5
DOIs
Publication statusPublished - May 2006

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