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

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 15N-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.

Molecular‐Level Insights into the Oxidative Degradation of Grafted Amines

“…A strong correlation at À254 ppm may indi- cate the presence of amide function; however, amide signal normally appears at a lower chemical shift (À270 ppm). [30] In addition, the signal at À254 ppm is correlated to the proton signal at 7.7-7.8 ppm (indicated by an asterisk) and is very similar to the one observed for TRI at À250 ppm ( Figure S3 in the Supporting Information). This could be assigned to the nitrogen atom in the following structure:…”

Brown carbon formation from ketoaldehydes of biogenic monoterpenes

“…Because the proposed C 18 H 23 NO 3 Schiff base is an organic compound containing both an imine group and a carboxylic acid group, strong intramolecular H-bonding (via a 7-member ring) may lead to zwitterion formation by protonation of the imine by the acid. 69 We note there are other reaction pathways leading to a C 18 H 23 NO 3 molecule stemming from the observed compounds in aqueous media, such as organic acidcatalysed Mannich-type reaction between enols and imines 70,71 or transimination of an imine and amine. [72][73][74] However, the proposed reaction mechanism satises the following criteria: it requires only mild organic acid catalysis and it occurs in aqueous solution.…”