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.
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 (J). Optimized geometrie...
| Publicado en: | Journal of the American Chemical Society Vol. 134; no. 36; pp. 14772 - 14781 |
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| Autores principales: | , , , , |
| Formato: | Artículo |
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American Chemical Society
9/12/2012
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=80073750&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 80073750 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 9/12/2012 vid: 134 iid: 36 pid: 997 pub: American Chemical Society artinfo: ui: 80073750 10.1021/ja302133s ppf: 14772 ppct: 9 formats: tig: atl: 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. aug: au: Garza, Alejandro J. Nag, Mrinmoy Carroll, William R. Goddard III, William A. Roberts, John D. affil: Crellin Laboratory of Chemistry, California Institute of Technology, Pasadena, California 91125, United States Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, United States su: Conformational analysis Dicarboxylic acids Dimethyl sulfoxide Density functionals Mathematical models Quantum theory Nuclear magnetic resonance spectroscopy Ionization (Atomic physics) Cyclohexane derivatives sug: subj: Conformational analysis Dicarboxylic acids Dimethyl sulfoxide Density functionals Mathematical models Quantum theory Nuclear magnetic resonance spectroscopy Ionization (Atomic physics) Cyclohexane derivatives ab: 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 (J). 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/K) indicated an absence of intramolecular H-bonding because K/K 10 (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/K increased drastically in DMSO (K/K = 4 × 10), where J and the ratio K/K = 10, K 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. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2012 holdings: @attributes: islocal: N |
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