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Energetics of a Low Barrier Hydrogen Bond in Nonpolar Solvents

Authors: Julius Rebek; and Leticia M. Toledo; Yoko Kato;

Energetics of a Low Barrier Hydrogen Bond in Nonpolar Solvents

Abstract

A measure of the strength of a low barrier hydrogen bond (LBHB) in apolar organic media was obtained using synthetic molecules derived from Kemp's triacid. The structures feature unusually rigid conformations that enforce intramolecular hydrogen bonds in a dicarboxylic acid, its corresponding acid-amide and their respective conjugate bases. Analysis of proton and deuterium NMR spectra established the formation of a LBHB in the conjugate base of the diacid and a conventional hydrogen bond in the conjugate base of the acid-amide. Through deprotonation equilibria with organic bases, it was determined that the conjugate base of the diacid was more stable than the conjugate base of the acid-amide by 2.4 kcal/mol in benzene and 1.4 kcal/mol in dichloromethane. These figures set the upper limits for the free energy of the additional stabilization arising from the LBHB at 25 °C. This value is far lower than many estimates but is closer to the recent determinations of Schwartz and Drueckhammer [J. Am. Chem. Soc. 1...

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
62
Average
Top 10%
Top 10%
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