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Published March 2006 | public
Journal Article

Conformational analyses of 2,3-dihydroxypropanoic acid as a function of solvent and ionization state as determined by NMR spectroscopy

Abstract

Vicinal ¹H-¹H coupling constants were used to determine the conformational preferences of 2,3-dihydroxypropanoic acid (1) (DL-glyceric acid) in various solvents and its different carboxyl ionization states. The stereospecific assignments of J₁₂ and J₁₃ were confirmed through the point-group substitution of the C-3 hydrogen with deuterium, yielding rac-(2SR,3RS)-[3-²H]-1, and the observation of only J₁₃ in the ¹H NMR spectra. While hydrogen bonding and steric strain may be expected to drive the conformational equilibrium, their role is overshadowed by a profound gauche effect between the vicinal hydroxyl groups that mimics other substituted ethanes, such as 1,2-ethanediol and 1,2-difluoroethane. At low pH, the conformational equilibrium is heavily weighted toward the gauche-hydroxyl rotamers with a range of 81% in DMSO-d₆ to 92% in tert-butyl alcohol-d₁₀. At high pH, the equilibrium exhibits a larger dependence upon the polarity and solvating capability of the medium, although the gauche effect still dominates in D₂O, 1,4-dioxane-d₈, methanol-d₄, and ethanol-d₆ (96, 89, 85, and 83% gauche-hydroxyls respectively). The observed preference for the gauche-hydroxyl rotamers is believed to stem primarily from hyperconjugative σC-H → σ*C-OH interactions.

Additional Information

© 2006 John Wiley & Sons, Ltd. Received 14 October 2005; Accepted 26 October 2005. Article first published online: 14 Feb 2006. Acknowledgement is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for support of this research. We are also deeply indebted to the National Science Foundation (CHE-0104273), 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, the E. I. DuPont Company, Merck, Dr and Mrs Chester M. McCloskey and Edith M. Roberts for their helpful financial assistance.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023