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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.
MedLine Citation:
PMID:  23210831     Owner:  NLM     Status:  Publisher    
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 (DeltadeltaH = 7.43 ppm) observed at -60 degrees C was indicative of intramolecular hydrogen bonding in 1A, which was later corroborated by determining the ratio of the first (K1) to the second (K2) ionization constants. K1/K2 in DMSO (1.3 × 107) was significantly larger than the value in water (2 × 10). In addition, K1/KE = 200 (where KE 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 1,3-cis-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.
Bright U Emenike; William R Carroll; John D Roberts
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-12-4
Journal Detail:
Title:  The Journal of organic chemistry     Volume:  -     ISSN:  1520-6904     ISO Abbreviation:  J. Org. Chem.     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2012-12-5     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985193R     Medline TA:  J Org Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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