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Conformational Preferences of cis-1,3-Cyclopentanedicarboxylic Acid and Its Salts by ^1H NMR Spectroscopy: Energetics of Intramolecular Hydrogen Bonds in DMSO

Emenike, Bright U. and Carroll, William R. and Roberts, John D. (2013) Conformational Preferences of cis-1,3-Cyclopentanedicarboxylic Acid and Its Salts by ^1H NMR Spectroscopy: Energetics of Intramolecular Hydrogen Bonds in DMSO. Journal of Organic Chemistry, 78 (5). pp. 2005-2011. ISSN 0022-3263.

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The conformational populations of cis-1,3- cyclopentanedicarboxylic acid (1) and its mono- and dianion were established in DMSO solution by comparing the vicinal proton−proton coupling constants (^3JHH) obtained in solution to their theoretical counterparts. Geometries used for ^3JHH theoretical estimation (using Karplus-type equations) were obtained from optimized structures at the B3LYP/6-31G-(2d,2p) level. The diacid (1) adopted many conformations, whereas the ionized species (1A mono- and 1B dianion) assumed single conformations. A downfield chemical shift of 19.45 ppm (Δδ_H = 7.43 ppm) observed at −60 °C was indicative of intramolecular hydrogen bonding in 1A, which was later corroborated by determining the ratio of the first (K_1) to the second (K_2) ionization constants. K_1/K_2 in DMSO (1.3 × 10^7) was significantly larger than the value in water (2 × 10). In addition, K_1/K_E = 200 (where K_E is the acidity constant of the monomethylester of 1) was greater than the intramolecular hydrogen bonding threshold value of 2. The calculated intramolecular hydrogen bond strength of 1A was ∼3.1 kcal mol^(−1), which is ∼2.7 kcal mol^(−1) more stable than the values for cis- 1,3-cyclohexanedicarboxylic acid (2A). Thus, the relative energies of intramolecular hydrogen bonding in the monoanions 1A and 2A suggests that 1,3-diaxial conformers are more favored for cyclopentane than for cyclohexane rings.

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Additional Information:© 2012 American Chemical Society. Published In Issue March 01, 2013. Article ASAP January 14, 2013. Just Accepted Manuscript. December 04, 2012. Publication Date (Web): December 4, 2012. Special Issue: Howard Zimmerman Memorial Issue. Acknowledgement is made to the National Science Foundation under Grants CHE-0543620 and TG-CHE1000106 and to the donors of the Petroleum Research Fund administered by the American Chemical Society for support for this research. Other important support came from the Summer Undergraduate Research Fellowship Program (SURF) at the California Institute of Technology, the Senior Scientist Mentor Program of the Camille and Henry Dreyfus Foundation, and the NORAC grant to Caltech by Dr. and Mrs, Chester M. McCloskey. We are indebted to Merck and Company, Dr. David J. Mathre, and Edith M. Roberts for their helpful financial assistance. The facilities of the MCS used in these studies were established with grants from DURIP-ONR and DURIP-ARO, with additional support from ONR, ARO, NSF, NIH, DOE, Chevron, Nissan, Dow Corning, Intel, Pfizer, Boehringer-Ingelheim, and Sanofi-Aventis. The authors declare no competing financial interest.
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American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship Program (SURF)UNSPECIFIED
Camille and Henry Dreyfus Foundation Senior Scientist Mentor ProgramUNSPECIFIED
Merck & CompanyUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
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Official Citation:Conformational Preferences of cis-1,3-Cyclopentanedicarboxylic Acid and Its Salts by 1H NMR Spectroscopy: Energetics of Intramolecular Hydrogen Bonds in DMSO Bright U. Emenike, William R. Carroll, and John D. Roberts The Journal of Organic Chemistry 2013 78 (5), 2005-2011
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37932
Deposited By: Ruth Sustaita
Deposited On:15 Apr 2013 17:16
Last Modified:15 Apr 2013 17:16

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