Effect of pH on carbon-13 NMR spectra of N-dodecyl-N, N-dimethylamine oxide solution

✍ Scribed by Bogumil Brycki; Miroslaw Szafran

• Book ID: 102950315
• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 509 KB
• Volume: 30
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260300614

✦ Synopsis

Abstract

Carbon‐13 NMR chemical shifts of the non‐ionic‐cationic surfactant N‐dodecyl‐N, N‐dimethylamine oxide (C~12~DAO) were measured and identified by an INADEQUATE experiment. On micellization, downfield chemical shifts were found for all carbon atoms except NCH~2~. The shifts are most pronounced for the carbon atoms in the central part of the chain. Protonation of the micelles resulted in upfield shifts of all the carbon atoms; the magnitudes decreased with increasing distance from the nitrogen atom. A plot of several chemical shifts against pH gave titration curves and p__K__~a~ values. The p__K__~a~ values vary with the carbon atom used in the calculation (from p__K__~a~ = 5.05 to 5.66). An AMI calculation of charge densities suggests that these variations in p__K__~a~ are caused by the electric field of the OH group. The effect of N‐oxidation on the chemical shifts of the carbon atoms in five solvents was estimated.