NDLI: Instability of 2,2-di(pyridin-2-yl)acetic acid. Tautomerization versus decarboxylation

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Instability of 2,2-di(pyridin-2-yl)acetic acid. Tautomerization versus decarboxylation

Content Provider	PubMed Central
Author	Borowski, Piotr Gawinecki, Ryszard Anna, Miłaczewska Skotnicka, Agnieszka Woliński, Krzysztof Brzyska, Agnieszka
Abstract	The DFT calculations at the B3LYP level with 6-311G** basis set were carried out in order to reveal whether tautomerization or decarboxylation is responsible for the instability of 2,2-di(pyridin-2-yl)acetic (DPA) and 1,8-diazafluorene-9-carboxylic (DAF) acids. The carboxyl protons in both compounds are involved in the intramolecular hydrogen bonds (the pyridine nitrogen atoms are the hydrogen bond acceptors). Although formation of two intramolecular OH···N hydrogen bonds in the enols of both carboxylic acids enables effective electron delocalization within the quasi rings (···HO − C = C − C = N), only ene-1,1-diol of DAF has somewhat lower energy than DAF itself (ΔE is ca. 7 kcal mol-1). DPA and its enediol have comparable energies. Migration of the methine proton toward the carbonyl oxygen atom (to form enediols) requires overstepping the energy barriers of 55-57 kcal mol-1 for both DPA and DAF. The enaminone tautomers of the acids, formed by migration of this proton toward the pyridine nitrogen atom, are thermodynamically somewhat more stable than the respective enediols. The energy barriers of these processes are equal to ca. 44 and 62 kcal mol-1 for DPA and DAF, respectively. Thus, such tautomerization of the acids is not likely to proceed. On the other hand, the distinct energetic effects (ca. 15 kcal mol-1) favor decarboxylation. This process involves formation of (E)-2-(pyridin-2(1H)-ylidenemethyl)pyridine and its cyclic analogue followed by their tautomerization to (dipyridin-2-yl)methane and 1,8-diazafluorene, respectively. Although the later compound was found to be somewhat thermodynamically more stable, kinetic control of tautomerization of the former is more distinct.
Related Links	http://dx.doi.org/10.1007/s00894-010-0780-y
Ending Page	868
Page Count	12
Starting Page	857
File Format	PDF
ISSN	16102940
e-ISSN	09485023
Journal	Journal of Molecular Modeling
Issue Number	4
Volume Number	17
Language	English
Publisher	Springer-Verlag
Publisher Date	2011-04-01
Access Restriction	Open
Rights Holder	Springer-Verlag
Subject Keyword	Physical and Theoretical Chemistry Inorganic Chemistry Organic Chemistry Computational Theory and Mathematics Catalysis Computer Science Applications Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Organic Chemistry Physical and Theoretical Chemistry Computational Theory and Mathematics Catalysis Inorganic Chemistry Computer Science Applications

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