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Comparison of the acis-base properties of 5- and 6-uracilmethylphosphonate (5Umpa2- and 6Umpa2-) and some related compounds. Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N1)H and the phosphonate group of 6Umpa2-


Moreno-Luque, C F; Freisinger, Eva; Griesser, R; Ochocki, J; Lippert, Bernhard; Sigel, H (2001). Comparison of the acis-base properties of 5- and 6-uracilmethylphosphonate (5Umpa2- and 6Umpa2-) and some related compounds. Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N1)H and the phosphonate group of 6Umpa2-. Royal Chemical Society. Journal. Perkin Transactions 2, 10:2005-2011.

Abstract

The acidity constants of 5-uracilmethylphosphonic acid, H2(5Umpa), and 6-uracilmethylphosphonic acid, H2(6Umpa), were determined by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 M, NaNO3). Comparison of these constants with those of related uracil derivatives (partly taken from the literature) allows the conclusion that an intramolecular hydrogen bond is formed between (N1)H and the phosphonate group of 6Umpa2−; the formation degree of this hydrogen-bonded isomer is estimated to be 86 ± 7%. The X-ray crystal structure analysis of H2(6Umpa) is reported but this solid state structure is dominated by intermolecular hydrogen bonds. In the context of the properties of 5Umpa2− and 6Umpa2− those of uracil are also discussed and from various comparisons of acidity constants it is concluded that deprotonation of uracil may occur at (N3)H as well as at (N1)H but that the (N3)-deprotonated species dominates with about 80% in aqueous solution at 25 °C and I = 0.1 M (Na+). The search for other examples of uracil derivatives which allow hydrogen-bond formation in aqueous solution has led to orotic acid (= 6-uracilcarboxylic acid; [H(6Urca)]) and 5-uracilcarboxylic acid [H(5Urca)]; based on acidity constant comparisons it is concluded that in aqueous solution (25 °C; I = 0.1 M, KCl) H(5Urca) exists to about 92 ± 10% as a species with a hydrogen bond between (C5)COOH and (C4)O, and 6Urca− to about 95 ± 5% as a species with a hydrogen bond between (C6)COO− and (N1)H. The importance of intramolecular hydrogen-bond formation to the acid–base properties of compounds in solution is briefly emphasized.

Abstract

The acidity constants of 5-uracilmethylphosphonic acid, H2(5Umpa), and 6-uracilmethylphosphonic acid, H2(6Umpa), were determined by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 M, NaNO3). Comparison of these constants with those of related uracil derivatives (partly taken from the literature) allows the conclusion that an intramolecular hydrogen bond is formed between (N1)H and the phosphonate group of 6Umpa2−; the formation degree of this hydrogen-bonded isomer is estimated to be 86 ± 7%. The X-ray crystal structure analysis of H2(6Umpa) is reported but this solid state structure is dominated by intermolecular hydrogen bonds. In the context of the properties of 5Umpa2− and 6Umpa2− those of uracil are also discussed and from various comparisons of acidity constants it is concluded that deprotonation of uracil may occur at (N3)H as well as at (N1)H but that the (N3)-deprotonated species dominates with about 80% in aqueous solution at 25 °C and I = 0.1 M (Na+). The search for other examples of uracil derivatives which allow hydrogen-bond formation in aqueous solution has led to orotic acid (= 6-uracilcarboxylic acid; [H(6Urca)]) and 5-uracilcarboxylic acid [H(5Urca)]; based on acidity constant comparisons it is concluded that in aqueous solution (25 °C; I = 0.1 M, KCl) H(5Urca) exists to about 92 ± 10% as a species with a hydrogen bond between (C5)COOH and (C4)O, and 6Urca− to about 95 ± 5% as a species with a hydrogen bond between (C6)COO− and (N1)H. The importance of intramolecular hydrogen-bond formation to the acid–base properties of compounds in solution is briefly emphasized.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2001
Deposited On:18 Apr 2013 09:08
Last Modified:05 Apr 2016 16:40
Publisher:Royal Society of Chemistry
ISSN:1472-779X
Publisher DOI:https://doi.org/10.1039/b101078f

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