Hindered rotation through intramolecular hydrogen-bonding: Opening statements on dimedone-aldehyde adducts

Forsén, Sture; Frankle, William E; Laszlo, Pierre; Lubochinsky, Janine

doi:10.1016/0022-2364(69)90071-7

Cited by 4 publications

(2 citation statements)

References 22 publications

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“…For comparison, the ring flip barrier for dimedone analogues in the same pair of solvents differs by about 6 kcal/mol. 23 The ΔG ‡ value for 2f is somewhat out, which probably is due to the interaction of NH protons with the N atom of pyridyl during the ring flip. We will return to this issue below, when discussing the results of DFT calculations.…”

Section: ■ Discussionmentioning

confidence: 98%

Hydrogen Bonding in Bis(6-amino-1,3-dimethyluracil-5-yl)-methane Derivatives: Dynamic NMR and DFT Evaluation

2016

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Three bis(6-amino-1,3-dimethyluracil-5-yl)-methane derivatives were studied experimentally by variable-temperature (1)H NMR in polar aprotic solutions (CD2Cl2, C5D5N, C2D2Cl4) and computationally by DFT. The unusual for diarylmethanes coplanar conformation of dimethyluracil rings of each molecule is held by a pair of unequal intramolecular N-H···O hydrogen bonds. We show the presence of two dynamic processes involving breakage/formation of these bonds. First, it is two independent NH2 group rotations, each coupled to nitrogen inversion. Second, it is uracil ring rotations (ring flips). The thermodynamic parameters (ΔH(‡), ΔS(‡), and ΔG(‡)) of both processes were estimated by the full line shape analysis of NMR signals and also by DFT calculations. We demonstrate that, though the ring flips exchange pairs of NH protons, the two processes are not coupled: during the ring flip NH2 groups do not rotate, and during the NH2 rotation the rings do not necessarily rotate. Unlike in many other diarylmethanes, the ring flips in the studied compounds are happening stepwise; i.e., the configuration when both rings are "in flight" at the same time is energetically unfavorable (small degree of "cog wheel effect"). The signs of the ΔS(‡) values indicate that the molecular flexibility increases during the NH2 rotations, but decreases during the ring flips.

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Section: ■ Discussionmentioning

confidence: 98%

Hydrogen Bonding in Bis(6-amino-1,3-dimethyluracil-5-yl)-methane Derivatives: Dynamic NMR and DFT Evaluation

2016

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“…All three situations were found to be present in the dicoumarols. methones (9). In fact, the assignment should be reversed: the low-field signal is syn in relation to R, and the interpretation is unambiguous as indicated in Table 1.…”

Section: Introductionmentioning

confidence: 93%

A stereodynamic investigation of antivitamins K in the dicoumarol series. II. Differentiation between the two hydroxyl groups by the nuclear Overhauser effect

Laruelle¹,

Godfroid²

1976

Can. J. Chem.

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. Can. J . Chem. 54, 813 (1976). Dicoumarol derivatives, substituted at the bridgehead, show a double restricted rotation. This hindered rotation is manifest through the appearance of two signals, the hydroxyl protons being diastereotopic at low temperatures.In this work we assign the two respective signals by the nuclear Overhauser effect. The highfield signal corresponds to a hydroxyl site close to the bridgehead tertiary proton, while the other corresponds to a site in proximity to the substituent R. The case of structurally analogous dimethones has been investigated by the same technique with identical conclusions. This disproves the interpretation made previously on the basis of steric and anisotropic effects.The interatomic distances concerned have been calculated, and these have yielded an estimate of deformations induced by the bridgehead substituents.Evidence is supplied for the different behavior of the two sites and this study gives evidence for a very facile intermolecular chemical exchange of the hydroxyl site close to the tertiary bridgehead proton in the presence of traces of protonated compounds.The overall behavior is the result of the asymmetry of the molecules of this series in their chelated form.CLAUDE LARUELLE ET JEAN-JACQUES GODFROID. Can. J. Chem. 54, 813 (1976).Les derives du dicoumarol, substitues au niveau du pont presentent une double rotation restreinte qui se manifeste par I'apparition de deux signaux, les protons hydroxyles etant diastereotropiques a basse temperature.La presente publication permet d'attribuer, par effet Overhauser nucleaire, les deux signaux aux groupes hydroxyles incrimines. Le signal a haut champ correspond au site hydroxyle proche du proton tertiaire du pont, alors que I'autre correspond au site proche du substituant R. D'autre part, le cas des dimethones, analogues structuraux, a ete etudie par la meme technique et ies conclusions sont identiques, ce qui annule l'interpretation inverse qui a ete faite anterieurement a partir d'interpretations steriques et anisotropiques. Les distances interatomiques concernees ont ete calculCeset les deformations induites par les substituants du pont estimees.Le comportement differencie des deux sites est mis en evidence et I'etude conclut a un echange chimique intermoleculaire tres facile du site hydroxyle proche du proton tertiaire du pont avec des traces d e composes protones.L'ensemble des proprietes mises en evidence est la consequence de I'asymetrie des molecules de cette serie dans leur forme chelatee.

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Rates and Kinetics of Hydrogen‐Bonding

Maeyer

1971

Israel Journal of Chemistry

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The experimental techniques for the study of the extremely fast reactions of hydrogen‐bond formation are reviewed. Direct high field dielectric and acoustic techniques as well as indirect NMR and dielectric methods are available; examples of their application to specific problems are given. Bond formation and bond transfer reactions must be distinguished. The mechanism of bond transfer can be of different types, similar to the associative and dissociative types of substitution mechanisms that were formulated for other classes of reactions.

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Hindered rotation through intramolecular hydrogen-bonding: Opening statements on dimedone-aldehyde adducts

Cited by 4 publications

References 22 publications

Hydrogen Bonding in Bis(6-amino-1,3-dimethyluracil-5-yl)-methane Derivatives: Dynamic NMR and DFT Evaluation

Hydrogen Bonding in Bis(6-amino-1,3-dimethyluracil-5-yl)-methane Derivatives: Dynamic NMR and DFT Evaluation

A stereodynamic investigation of antivitamins K in the dicoumarol series. II. Differentiation between the two hydroxyl groups by the nuclear Overhauser effect

Rates and Kinetics of Hydrogen‐Bonding

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