π-Electron delocalisation in the spacer of the O-H…N bridge in Schiff bases. Crystal and molecular structure of 3,5-dimethoxy-2 [(phenylimino) methyl]phenol and 4-methoxy-2-[(phenylimino) methyl] phenol

Krygowski, Tadeusz M.; Stępień, Beata T.; Anulewicz‐Ostrowska, Romana; Dziembowska, Teresa

doi:10.1016/s0040-4020(99)00192-1

Cited by 14 publications

(11 citation statements)

References 10 publications

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“…A much more representative sample ( n = 47) of experimental geometries of ortho -hydroxy Schiff bases was used to study π-electron delocalization of the spacer built up of NC and two CC and CO bonds between the H-bond-donating OH group and H-bond-accepting nitrogen atom in the CN bond, leading to a similar conclusion. Moreover, no dependence of HOMA on the N···O interatomic distance was found …”

Section: 5 Intramolecular H-bond Systemsmentioning

confidence: 93%

Interrelation between H-Bond and Pi-Electron Delocalization

2005

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Section: 5 Intramolecular H-bond Systemsmentioning

confidence: 93%

Interrelation between H-Bond and Pi-Electron Delocalization

2005

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“…Syntheses : 4-Methoxy-, 3-methoxy-, 5-methoxy-, and 4,6-dimethoxysalicylaldehydes were purchased from Aldrich Chemicals. Schiff bases were obtained by the standard method of condensation of the substituted salicylaldehydes with the corresponding amines in refluxing ethanol: N -(R-salicylidene)−methylamines R = 4,6-di-OCH 3 ( 1 ), R = 4-OCH 3 ( 4 ), R = 3-OCH 3 ( 10 ), R = 5-OCH 3 ( 12 ) by condensation of respective salicylaldehydes with methylamine; N -(4-OCH 3 -salicylidene)−butylamine ( 2) by condensation of 4-methoxysalicylaldehyde with butylamine (mp: 43−45 °C); N -(4,6-di-OCH 3 -salicylidene)-aniline ( 7 ) by condensation of respective aldehyde with aniline …”

Section: Methodsmentioning

confidence: 99%

Keto Forms of Salicylaldehyde Schiff Bases: Structural and Theoretical Aspects

et al. 2006

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Twelve Schiff bases of methoxy-substituted salicylaldehyde have been examined by crystallographic and spectroscopic methods, as well as by DFT theoretical calculations in order to investigate the effect of the substituent's position on the keto-enol equilibrium in the crystalline state. Four out of the 10 structurally characterized compounds with methoxy substitution on the para and/or ortho positions with respect to the aldimine bridge and deriving from aliphatic amines or alkylarylamines are found as cis-keto tautomers and form dimers. In contrast, the five pure enol tautomers derive either from aliphatic or alkylarylamines and are meta substituted or from aniline or benzylamine and are para and/or ortho methoxy substituted. The DFT calculations support the crystallographic results and, moreover, they have shown that keto and enol tautomers are affected differently by the relative arrangement of the monomers. Overall, the DFT calculations point to a plausible hypothesis for the stabilization of the keto form in the crystalline state: In cases with a sufficiently low enol-keto energy difference of the isolated monomers, as when the methoxy group is at ortho and/or para positions with respect to the aldimino group, extra stabilization of the keto form is derived from molecular association, thus leading to its crystallization.

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“…Conversion of both equations into the logarithmic form of eq leads to eq , where c = a – b . In a strict sense, however, the imino and phenolic groups do not act independently, since they are connected through a spacer that allows a continuous delocalization between them and, in addition, united to each other by the hydrogen bonding. Gilli et al have suggested that Schiff bases derived from salicylaldehydes are a fine example of synergy between the strength of the hydrogen bond and the degree of π-delocalization, whereas Krygowski et al state that the most important factor affecting the delocalization of π-electrons through the linker is the effect of groups attached to the ring, one of whose bonds is part of the spacer itself. In addition, Solà et al indicate that the effect of the substituents and the effect of the mesomeric assistance on the hydrogen bond are mutually cooperative, and both effects can then be treated as components of the same phenomenon.…”

Section: Resultsmentioning

confidence: 99%

Imine or Enamine? Insights and Predictive Guidelines from the Electronic Effect of Substituents in H-Bonded Salicylimines

et al. 2020

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Imine and enamine bonds decorate the skeleton of numerous reagents, catalysts, and organic materials. However, it is difficult to isolate at will a single tautomer, as dynamic equilibria occur easily, even in the solid state, and are sensitive to electronic and steric effect, including π-conjugation and H-bonding. Here, using as model Schiff bases generated from salicylaldehydes and TRIS in a set of linear free energy relationships (LFER), we disclose how the formation of either imines or enamines can be controlled and provide a comprehensive framework that captures the structural underpinning of this prediction. This work highlights the potentiality of tailor-made designs en route to compounds with desirable functionality.

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π-Electron delocalisation in the spacer of the O-H…N bridge in Schiff bases. Crystal and molecular structure of 3,5-dimethoxy-2 [(phenylimino) methyl]phenol and 4-methoxy-2-[(phenylimino) methyl] phenol

Cited by 14 publications

References 10 publications

Interrelation between H-Bond and Pi-Electron Delocalization

Interrelation between H-Bond and Pi-Electron Delocalization

Keto Forms of Salicylaldehyde Schiff Bases: Structural and Theoretical Aspects

Imine or Enamine? Insights and Predictive Guidelines from the Electronic Effect of Substituents in H-Bonded Salicylimines

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