- Synthesis and Acidity Constants of 13CO2H-Labelled Dicarboxylic Acids. pKas from 13C-NMR
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Simple dicarboxylic acids: adipic (1), succinic (2) and malonic (3); more complex linear tetrapyrroles with two propionic acid groups: mesobiliverdin-XIIIα (4) and mesobilirubin-XIIIα (5), and a rubin analog with a gemdimethyl at C10 (6) were prepared with 99% 13C-enrichment in their CO2H groups. Their pKa values were determined from titration curves in water and in H2O-(CD3)2SO solutions: plots of carboxyl carbon 13C-NMR chemical shifts with varying pH. Titration curves of diacids 1-3 with known pKa's in H2O served as calibration standards for determination of pKas of tetrapyrrole diacids 4-6: pKa1 = 3.9, pKa2 = 5.3 for 4; pKa1 = 4.2, pKa2 = 4.9 for 5, and pKa1 = 4.7, pKa2 = 5.7 for 6 in H2O. Copyright
- Holmes, Darren L.,Lightner, David A.
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- A bicyclic ketone as a solid-state 13C NMR intensity reference
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The synthesis and NMR relaxation properties of 4-(N-methylpyrrolidino)bicyclo[3.2.1]octan-8-one triflate (321) are described. The use of 13CO-enriched 321 as a 13C intensity reference is justified and demonstrated. The dominant 13C peak in 321-13CO is 217 ppm, far from most other 13C chemical shifts of diamagnetic organic compounds. Hence, this intensity reference peak avoids peak overlap problems for most organic compounds.
- Hall, Randal A.,Jurkiewicz, Antoni,Maciel, Gary E.
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p. 534 - 538
(2007/10/02)
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