Conformational Preferences of 3-(Dimethylazinoyl)propanoic Acid as a Function of pH and Solvent; Intermolecular versus Intramolecular Hydrogen Bonding
Abstract
The conformational equilibrium of 3-(dimethylazinoyl)propanoic acid (DMAPA, azinoyl = N^+(O^−) has a weak pH-dependence in D_2O, with a slight preference for trans in alkaline solutions. The acid ionization constants of the protonated amine oxide and carboxylic functional groups as determined by NMR spectroscopy were 7.9 × 10^(−4) and 6.3 × 10^(−6), respectively. The corresponding value of K_1/K_2 of 1.3 × 10^2 is not deemed large enough to provide experimental NMR evidence for a significant degree of intramolecular hydrogen bonding in D_2O. Conformational preferences of DMAPA are mostly close to statistical (gauche/trans = 2/1) in other protic solvents, e.g., alcohols. However, the un-ionized form of DMAPA appears to be strongly intramolecularly hydrogen-bonded and gauche in aprotic solvents.
Additional Information
© 2009 American Chemical Society. Received November 6, 2008. Publication Date (Web): February 26, 2009 Acknowledgement is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for their support of this research. This material here is also based upon work supported by the National Science Foundation under Grant CHE-0543620, the Summer Undergraduate Research Fellowship Program (SURF) at the California Institute of Technology, and the Senior Scientist Mentor Program of the Camille and Henry Dreyfus Foundation. In addition, we are indebted to Merck & Company, Dr. & Mrs. Chester M. McCloskey, Dr. David J. Mathre, and Edith M. Roberts for their helpful financial assistance. The authors wish to thank Dr. Scott Ross and Maya Popova for their help and guidance. Supporting Information Available: Characterization, computational data, and Altona equations used for the calculations of percent gauche of DMAPA in protic and aprotic solvents. Also included is the unpublished research by P.V. Jog.2 This material is available free of charge via the Internet at http://pubs.acs.org.Attached Files
Supplemental Material - Nkansah2009p71610.1021jo802488k_supp.pdf
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Additional details
- Eprint ID
- 15597
- DOI
- 10.1021/jo802488k
- Resolver ID
- CaltechAUTHORS:20090904-083008660
- NSF
- CHE-0543620
- Summer Undergraduate Research Fellowship Program (SURF)
- Camille and Henry Dreyfus Foundation
- Created
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2009-09-23Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field