Structural Studies by Nuclear Magnetic Resonance. VIII. Ring-Substituted Phenylhydrazones, Semicarbazones, and Thiosemicarbazones

Karabatsos, Gerasimos J.; Vane, Floie M.; Taller, Robert A.; Hsi, Nelson

doi:10.1021/ja01070a029

Cited by 116 publications

(34 citation statements)

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“…Loss of phenyl conjugation with the CN double bond can be mitigated by conjugative stabilization of the non-bonded electron pair at nitrogen, such that even the smallest substituents other than hydrogen can induce non-orthogonality. This perpendicular conformation is, however, not favoured in aldehyde anils,,); therefore, I d of coplanar phenyl has to be used to explain the highly prepondering E-anils (entries 55 and 68) of those aldehydes for which measurable E/Z ratios were found in Nalkylimines (entries 54 and 62 -66).…”

Section: B Discussionmentioning

confidence: 99%

Empirical Substituent Parameters for E/Z Equilibrium Constants

Knorr

1980

Chem. Ber.

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A set of substituent parameters Ad is proposed which permits the prediction of E/Z equilibrium constants for olefins, enamines, Schiff bases, hydrazones, semicarbazones, oximes, and nitrones. The set includes values for the ,,non-bonded" electron pairs and the nitrone oxygen as well as for amino or phenyl groups coplanar and orthogonal to the double bond. Ketone anils prefer a perpendicular phenyl group. Principal limitations of the very simple heuristic model are discussed. The model is also applied to the ,,cis''-and ,,ortho"-effects, enolates, and Schiff bases of cyclic and bicyclic ketones. Empirische Substituentenparameter fur E/Z-Gleichgewichtskonstantenl)Ein vorgeschlagener Satz von Substituentenparametern Ad erlaubt die Vorhersage der E/Z-Gleichgewichtskonstanten bei Olefinen, Enaminen, Schiffschen Basen, Hydrazonen, Semicarbazonen, Oximen und Nitronen. Der Parametersatz enthalt Werte fur ,,nichtbindende" Elektronenpaare und Nitronsauerstoff sowie fur Amino-und Phenylgruppen, die koplanar oder orthogonal zur Doppelbindung gestellt sind. Phenylreste in Ketonanilen bevorzugen die Orthogonalkonformation. Grundsatzliche Beschrankungen des sehr einfachen heuristischen Modells werden besprochen. Es lafit sich anwenden auf den ,,cis''-und den ,,ortho"-Effekt, auf Enolate und Schiffsche Basen cyclischer und bicyclischer Ketone. E/Z isomerism2) of compounds 1 with various kinds of double (or partially double) bonds has frequently been studied by NMR spectroscopy. A systematic rationalization and hence interpretation of such a wealth of data could be valuable in predicting E/Z equilibrium ratios. Inspired by an apparently undeveloped early idea due to Ruch and Ugi3), I propose to utilize a very simple approach by which such equilibria can be calculated from a tentative set of substituent parameters Ad and sensitivity factors pd.Although the model to be described below does not involve chirality, it is formally akin to chirality functions3s4) which were occasionally used for quantitative descriptions of asymmetric induction4s5), conformational equilibria6), and optical rotations'). A. Procedure and ResultsNotations for the E-and Z-isomers2) of 1 are obtained by ordering the substituents Ri according to the priority8) sequence (R2 > R1 and R4 > R3 within each pair). The basic assumption is3) that the natural logarithm of the E/Z concentration ratio at thermal equilibrium may be calculated from eq. (1); i.e., from the product of differences of substituent parameters at double bonds, Ad(R).

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Section: B Discussionmentioning

confidence: 99%

Empirical Substituent Parameters for E/Z Equilibrium Constants

Knorr

1980

Chem. Ber.

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“…Karabatsos e colaboradores 50 mostraram, em estudos utilizando a técnica de RMN 1 H, que os hidrogênios azometina de tiossemicarbazonas na configuração E ressonam a campo magné-tico baixo em relação a tiossemicarbazonas em configuração Z, mesmo em diferentes solventes. Resultado semelhante foi obtido por Antonini e colaboradores 28 , alguns anos depois.…”

Section: Esquema 2 Análise Retrossintética De Tiossemicarbazonasunclassified

Tiossemicarbazonas: métodos de obtenção, aplicações sintéticas e importância biológica

Tenório¹,

Góes²,

Lima³

et al. 2005

Quím. Nova

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“…4 b there are additional resonances from the second isomer which may be used for configurational assignment. NMR studies on unsymmetrical hydrazones [12] have shown that the 'H resonance of a CH 3 group a to the C=N bond is generally shifted upfield when cis to the 2,4-dinitrophenyl group. This configuration applies to the anti isomer of MIBK-2,4-dinitrophenylhydrazone.…”

Section: Introductionmentioning

confidence: 99%

Syn/anti isomerization of 2,4-dinitrophenylhydrazones in the determination of airborne unsymmetrical aldehydes and ketones using 2,4-dinitrophenylhydrazine derivation

Binding

Müller

Witting

1996

Fresenius J Anal Chem

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Aldehydes and ketones readily react with 2,4-dinitrophenylhydrazine (2,4-DNPH) to form the corresponding hydrazones. This reaction has been frequently used for the quantification of airborne carbonyl compounds. Since unsymmetrical aldehydes and ketones are known to form isomeric 2,4-dinitrophenylhydrazones (syn/ anti-isomers), the influence of isomerization on the practicability and accuracy of the 2,4-DNPH-method using 2,4-dinitrophenylhydrazine-coated solid sorbent samplers has been studied with three ketones (methyl ethyl ketone (MEK), methyl isopropyl ketone (MIPK), and methyl isobutyl ketone (MIBK)). With all three ketones the reaction with 2,4-DNPH resulted in mixtures of the isomeric hydrazones which were separated by HPLC and GC and identified by mass spectroscopy and (1)H nuclear magnetic resonance spectroscopy. The isomers show similar chromatographic behaviour in HPLC as well as in GC, thus leading to problems in quantification and interpretation of chromatographic results.

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Structural Studies by Nuclear Magnetic Resonance. VIII. Ring-Substituted Phenylhydrazones, Semicarbazones, and Thiosemicarbazones

Cited by 116 publications

References 0 publications

Empirical Substituent Parameters for E/Z Equilibrium Constants

Empirical Substituent Parameters for E/Z Equilibrium Constants

Tiossemicarbazonas: métodos de obtenção, aplicações sintéticas e importância biológica

Syn/anti isomerization of 2,4-dinitrophenylhydrazones in the determination of airborne unsymmetrical aldehydes and ketones using 2,4-dinitrophenylhydrazine derivation

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