Solution and solid state (CPMAS) NMR studies of the tautomerism of six‐membered heterocyclic compounds related to 2‐pyridones

López, Concepcíon; Claramunt, R. M.; Alkorta, Ibón; Elguero, José

doi:10.1155/2000/421654

Cited by 21 publications

(12 citation statements)

References 22 publications

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“…In the alkyl series of 1a-1d (1e excluded due to polymorphic forms present) the C2 and C12 chemical shifts increase as the steric crowding increases whereas the shifts of C3 and C7 decrease (Me [ Et [ i-Pr). The C7 chemical shifts for 1a-1d, 1f, 1g are in agreement with the solid state data for 2-pyridone within ±1 ppm [47].…”

Section: Nmr Spectroscopysupporting

confidence: 85%

Intermolecular steric hindrance in 7-acylamino-[1H]-2-oxo-1,8-naphthyridines: NMR, ESI-MS, IR, and DFT calculation studies

et al. 2011

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Intermolecular interactions of 7-(RCONH)-[1H]-2-oxo-1,8-naphthyridines (R = Me, Et, i-Pr, t-Bu, 1-adamantyl (1-Ad), CF 3 , and C 2 F 5 ) containing ADAD quadruple hydrogen bonding motif were studied by liquid and solid state NMR, ESI-MS, IR, and DFT calculations. 1 H NMR was used to determine the dimerization constants of i-Pr and 1-Ad congeners in CDCl 3 . 13 C and 15 N crosspolarization (CP) magic angle spinning (MAS) NMR data suggest that compounds possess similar solid state structures. Further, mass spectral data reveal that in gas phase both Me and 1-Ad derivatives form also multimers due to lack of competitive solvent interactions. The structures of the gas phase multimers depend on the size of the alkyl group. These results are in agreement with quantum chemical calculations. Geometry optimization and 1 H NMR spectra show that in dimers that carry bulky alkyl groups (t-Bu and 1-Ad) certain hydrogen bonds are weaker than in Me, Et, and i-Pr derivatives while strong electron acceptors, CF 3 and C 2 F 5 , deshields hydrogen bonded protons but creates significant electronic F/O repulsion yielding lowering of the energy of interaction. The influence of steric effect on dimerization of quadruply hydrogen bonded dimers was correlated with the Taft E s values.

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Section: Nmr Spectroscopysupporting

confidence: 85%

Intermolecular steric hindrance in 7-acylamino-[1H]-2-oxo-1,8-naphthyridines: NMR, ESI-MS, IR, and DFT calculation studies

et al. 2011

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“…An NMR study revealed that the preference of each tautomeric form depends on its state, although no hydroxypyrimidine form has ever been observed. In the solid state, only the 3H-tautomer has been found, while in polar solvents, a mixture of 1H-and 3H-tautomers is observed (Ló pez et al, 2000). These results agree with the two crystal structures containing pyrimidin-4one in the Cambridge Structural Database (CSD, Version 5.31 of November 2009, plus four updates; Allen, 2002), which confirmed that the 3H-tautomer is preferred [CSD refcodes BAGQUV (Vaillancourt et al, 1998) and XOLHOW (Bhogala et al, 2008)].…”

Section: Commentsupporting

confidence: 73%

Pseudopolymorphs of 2,6-diaminopyrimidin-4-one and 2-amino-6-methylpyrimidin-4-one: one or two tautomers present in the same crystal

2011

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The derivatives of pyrimidin-4-one can adopt either a 1H- or a 3H-tautomeric form, which affects the hydrogen-bonding interactions in cocrystals with compounds containing complementary functional groups. In order to study their tautomeric preferences, we crystallized 2,6-diaminopyrimidin-4-one and 2-amino-6-methylpyrimidin-4-one. During various crystallization attempts, four structures of 2,6-diaminopyrimidin-4-one were obtained, namely solvent-free 2,6-diaminopyrimidin-4-one, C(4)H(6)N(4)O, (I), 2,6-diaminopyrimidin-4-one-dimethylformamide-water (3/4/1), C(4)H(6)N(4)O·1.33C(3)H(7)NO·0.33H(2)O, (Ia), 2,6-diaminopyrimidin-4-one dimethylacetamide monosolvate, C(4)H(6)N(4)O·C(4)H(9)NO, (Ib), and 2,6-diaminopyrimidin-4-one-N-methylpyrrolidin-2-one (3/2), C(4)H(6)N(4)O·1.5C(5)H(9)NO, (Ic). The 2,6-diaminopyrimidin-4-one molecules exist only as 3H-tautomers. They form ribbons characterized by R(2)(2)(8) hydrogen-bonding interactions, which are further connected to form three-dimensional networks. An intermolecular N-H···N interaction between amine groups is observed only in (I). This might be the reason for the pyramidalization of the amine group. Crystallization experiments on 2-amino-6-methylpyrimidin-4-one yielded two isostructural pseudopolymorphs, namely 2-amino-6-methylpyrimidin-4(3H)-one-2-amino-6-methylpyrimidin-4(1H)-one-dimethylacetamide (1/1/1), C(5)H(7)N(3)O·C(5)H(7)N(3)O·C(4)H(9)NO, (IIa), and 2-amino-6-methylpyrimidin-4(3H)-one-2-amino-6-methylpyrimidin-4(1H)-one-N-methylpyrrolidin-2-one (1/1/1), C(5)H(7)N(3)O·C(5)H(7)N(3)O·C(5)H(9)NO, (IIb). In both structures, a 1:1 mixture of 1H- and 3H-tautomers is present, which are linked by three hydrogen bonds similar to a Watson-Crick C-G base pair.

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“…Besides, we have published several papers where absolute shieldings (σ) calculated for isolated molecules are successfully compared with chemical shifts (δ) determined in the solid state by CPMAS NMR. [14][15][16] Relative stability of tautomers (3a) and (3b) We have reported in Table 1 the energetic results of the calculations. Tautomer 3b is 31.3 kJ mol -1 more stable than tautomer 3a, therefore, in the discussion of the CPMAS NMR chemical shifts only tautomer 3b will be considered.…”

Section: Cpmas Nmr Of Compounds (3) and (4)mentioning

confidence: 99%

High resolution NMR of free radicals: 13C magic angle spinning of two solid organic free radicals derived from 4,5-dihydro-1H-imidazol-3-oxide-1-oxyl and theoretical calculation of their NMR properties

María¹,

Claramunt²,

Vasilevsky³

et al. 2010

Arkivoc

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Solution and solid state (CPMAS) NMR studies of the tautomerism of six‐membered heterocyclic compounds related to 2‐pyridones

Cited by 21 publications

References 22 publications

Intermolecular steric hindrance in 7-acylamino-[1H]-2-oxo-1,8-naphthyridines: NMR, ESI-MS, IR, and DFT calculation studies

Intermolecular steric hindrance in 7-acylamino-[1H]-2-oxo-1,8-naphthyridines: NMR, ESI-MS, IR, and DFT calculation studies

Pseudopolymorphs of 2,6-diaminopyrimidin-4-one and 2-amino-6-methylpyrimidin-4-one: one or two tautomers present in the same crystal

High resolution NMR of free radicals: 13C magic angle spinning of two solid organic free radicals derived from 4,5-dihydro-1H-imidazol-3-oxide-1-oxyl and theoretical calculation of their NMR properties

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