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Conformational Preferences of trans-1,2- and cis-1,3- Cyclohexanedicarboxylic Acids in Water and Dimethyl Sulfoxide as a Function of the Ionization State As Determined from NMR Spectroscopy and Density Functional Theory Quantum Mechanical Calculations

Garza, Alejandro J. and Nag, Mrinmoy and Carroll, William R. and Goddard, William A., III and Roberts, John D. (2012) Conformational Preferences of trans-1,2- and cis-1,3- Cyclohexanedicarboxylic Acids in Water and Dimethyl Sulfoxide as a Function of the Ionization State As Determined from NMR Spectroscopy and Density Functional Theory Quantum Mechanical Calculations. Journal of the American Chemical Society, 134 (36). pp. 14772-14780. ISSN 0002-7863. http://resolver.caltech.edu/CaltechAUTHORS:20121115-072345769

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Abstract

The populations of diaxial (aa) and diequatorial (ee) conformers of trans-1,2- and cis-1,3-cyclohexanedicarboxylic acids (CDCAs; 1 and 2, respectively) and their salts were determined in water and dimethyl sulfoxide (DMSO) solutions from vicinal proton–proton NMR J couplings (3J_(HH)). Optimized geometries and free energies for these compounds were obtained at the M06-2X/cc-pVTZ(-f)++ level. Although carboxylic acid groups in cyclohexane rings are generally believed to be far more stable (~2 kcal/mol) in equatorial than axial positions, this investigation demonstrated that an aa conformation (normally assumed to be completely insignificant for these compounds) can be favored depending on the medium and ionization state: strong ee preferences (>90%) were observed in water and DMSO for both diacids and their salts, except for the dianion of 1 in DMSO, which was found to be substantially aa (~57%). The possibility of intramolecular hydrogen bonding (H-bonding) was also investigated; the ratios of the ionization constants (K_1/K_2) indicated an absence of intramolecular H-bonding because K_1/K_2 « 10^4 (a standard criterion for non-H-bonding in dicarboxylic acids) for both 1 and 2 in water and also for 2 in DMSO. For 1, K_1/K_2 increased drastically in DMSO (K_1/K_2 = 4 × 10^6), where ^3J_(HH) and the ratio K_1/K_E = 10, K_E being the acidity constant of the monomethyl ester of 1, indicated the formation of an intramolecular H-bond for the monoanion in this solvent. An explanation for the observation of compact dianions in solution in terms of the generalized Born equation is also provided.


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http://dx.doi.org/10.1021/ja302133sDOIArticle
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ORCID:
AuthorORCID
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2012 American Chemical Society. Received: March 19, 2012. Publication Date (Web): June 19, 2012. The authors declare no competing financial interest. We thank the National Science Foundation (Grants CHE-0543620 and TG-CHE100106) and 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 of Dr. & Mrs. Chester M. McCloskey. We are indebted to Merck & Co., Dr. David J. Mathre, and Edith M. Roberts for their helpful financial assistance. The facilities of the MSC 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. We would also like to thank Dr. Jose Luis Mendoza for providing valuable discussions and calculations that aided in the computational part of this project.
Funders:
Funding AgencyGrant Number
NSFCHE-0543620
NSFTG-CHE100106
American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Camille and Henry Dreyfus FoundationUNSPECIFIED
NORACUNSPECIFIED
Merck & CompanyUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
NIHUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
ChevronUNSPECIFIED
NissanUNSPECIFIED
Dow CorningUNSPECIFIED
IntelUNSPECIFIED
PfizerUNSPECIFIED
Boehringer-IngelheimUNSPECIFIED
Sanofi-AventisUNSPECIFIED
Record Number:CaltechAUTHORS:20121115-072345769
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20121115-072345769
Official Citation:Conformational Preferences of trans-1,2- and cis-1,3-Cyclohexanedicarboxylic Acids in Water and Dimethyl Sulfoxide as a Function of the Ionization State As Determined from NMR Spectroscopy and Density Functional Theory Quantum Mechanical Calculations Alejandro J. Garza, Mrinmoy Nag, William R. Carroll, William A. Goddard, III, and John D. Roberts Journal of the American Chemical Society 2012 134 (36), 14772-14780
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35469
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:15 Nov 2012 16:20
Last Modified:23 Aug 2016 10:21

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