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Issue 10, 2012
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The conformers of 3-fluoroalanine. A theoretical study§

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Abstract

Quantum chemical calculations (DFT, SCS-MP2) show that the relative energies of the four principal alanine conformations are only marginally altered by the introduction of a single fluorine substituent into the methyl group. The fluorinegauche effect and attractive interactions of fluorine to the O–H or N–H moieties (formation of hydrogen bridges) do stabilize particular conformers of 3-fluoroalanine. This is true for the neutral molecule both in the gas phase and in aqueous solution (CPCM-model), but also for the zwitterionic forms and the conformers of the related carboxylate ions and also for the respective ammonium ions in aqueous solution. In water (CPCM calculations), the zwitterion is almost equal in energy to the most stable conformer of the neutral 3-fluoroalanine. Compared to alanine the atomic charges of the amino group and the carboxyl function of 3-fluoroalanine are not significantly influenced by the fluorine at C3, which relates to the fact that both experimental pKa values are almost equal for alanine and 3-fluoroalanine.

Graphical abstract: The conformers of 3-fluoroalanine. A theoretical study

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Article information


Submitted
30 Aug 2011
Accepted
05 Dec 2011
First published
07 Dec 2011

Org. Biomol. Chem., 2012,10, 2084-2093
Article type
Paper

The conformers of 3-fluoroalanine. A theoretical study

I. Humelnicu, E. Würthwein and G. Haufe, Org. Biomol. Chem., 2012, 10, 2084
DOI: 10.1039/C2OB06492H

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