NMR, MP2, and DFT study of thiophenoxyketenimines (<i>o</i>‐thio‐Schiff bases): Determination of the preferred form

Saeed, Bahjat A.; Elias, Rita S.; Kamounah, Fadhil S.; Hansen, Poul Erik

doi:10.1002/mrc.4677

Cited by 8 publications

(7 citation statements)

References 23 publications

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“…The latter contributes quite considerably. The NH chemical shifts vary from 18.06 ppm for R and R′ = CH 3 to 19.26 ppm for R= PhN(CH 3 ) 2 and R′=CH 3 [ 43 ] or 17.33 ppm for CH 3 =PhCH 3 , R′=CH 3 or 18.2 ppm for R=PhOCH 3 and R′=CH 3 [ 44 ]. Similar values were also obtained for derivatives in which R′ is H [ 45 ].…”

Section: Nmrmentioning

confidence: 99%

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A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Hansen

2021

Molecules

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Intramolecular NH…O,S,N interactions in non-tautomeric systems are reviewed in a broad range of compounds covering a variety of NH donors and hydrogen bond acceptors. 1H chemical shifts of NH donors are good tools to study intramolecular hydrogen bonding. However in some cases they have to be corrected for ring current effects. Deuterium isotope effects on 13C and 15N chemical shifts and primary isotope effects are usually used to judge the strength of hydrogen bonds. Primary isotope effects are investigated in a new range of magnitudes. Isotope ratios of NH stretching frequencies, νNH/ND, are revisited. Hydrogen bond energies are reviewed and two-bond deuterium isotope effects on 13C chemical shifts are investigated as a possible means of estimating hydrogen bond energies.

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Section: Nmrmentioning

confidence: 99%

“…Taken from [ 42 ] For the thio-Schiff base resonance forms are demonstrated. Taken from [ 43 ]. The number is the NH chemical shift in ppm.…”

Section: Figurementioning

confidence: 99%

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Hansen

2021

Molecules

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“…In a simplified way, deuterium isotope effects can be calculated by assuming that the XH bond is shortened upon deuteration. This approach has been described in a number of papers [62,71,72,74]. The shortening can be determined by the calculation of the hydrogen bond potential, but this is time consuming [43,75].…”

Section: Theoretical Calculationsmentioning

confidence: 99%

Isotope Effects on Chemical Shifts in the Study of Hydrogen Bonds in Small Molecules

Hansen

2022

Molecules

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This review is giving a short introduction to the techniques used to investigate isotope effects on NMR chemical shifts. The review is discussing how isotope effects on chemical shifts can be used to elucidate the importance of either intra- or intermolecular hydrogen bonding in ionic liquids, of ammonium ions in a confined space, how isotope effects can help define dimers, trimers, etc., how isotope effects can lead to structural parameters such as distances and give information about ion pairing. Tautomerism is by advantage investigated by isotope effects on chemical shifts both in symmetric and asymmetric systems. The relationship between hydrogen bond energies and two-bond deuterium isotope effects on chemical shifts is described. Finally, theoretical calculations to obtain isotope effects on chemical shifts are looked into.

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“…DFT calculations of nuclear shieldings have been shown to be a useful tool in deciding between structures or helping in determining the composition of equilibrating structures. [6] However, calculations on anions may be difficult due to large selfinteractions errors. [7] Deuterium substitution is also investigated.…”

Section: Introductionmentioning

confidence: 99%

Azo‐hydrazone molecular switches: Synthesis and NMR conformational investigation

Kurutos

Kamounah

Dobrikov

et al. 2021

Magnetic Reson in Chemistry

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A series of five intramolecularly hydrogen-bonded arylhydrazone (aryl = phenol, p-nitrophenol, anisole, quinoline) derived molecular switches have been synthesized and characterized by NMR and HRMS techniques. It was found that the compounds exist as different isomers in solution. An investigation of both conformational and/or configurational changes of the azo-hydrazone compounds was carried out by 1D 1 H-and 13 C-spectra, 2D NOESY, COSY, HSQC, and HMBC techniques. It was found that these stimuli-responsive molecular switches exist mainly in the E form by intramolecularly hydrogen bonded between NH and the pyridine nitrogen at equilibrium. Deprotonation of the neutral E form yields the E 0 deprotonated isomer. Prediction of 13 C-NMR chemical shifts was achieved by DFT quantum mechanical calculations. Anions have traditionally been difficult to calculate correctly, so calculations of the anion using different functionals, basis sets, and solvent effects are also included. Deuterium isotope effects on the 13 C-NMR chemical shifts were employed in the assignments and furthermore utilized as indicators of intramolecular hydrogen bonding. Studies in various organic solvents including CDCl 3 , CD 3 CN, and DMSO-d 6 were also performed aiming to monitor dynamic changes over several days. The effect of the hydrogen bonded solvents leads to Z forms.

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NMR, MP2, and DFT study of thiophenoxyketenimines (o‐thio‐Schiff bases): Determination of the preferred form

Cited by 8 publications

References 23 publications

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Isotope Effects on Chemical Shifts in the Study of Hydrogen Bonds in Small Molecules

Azo‐hydrazone molecular switches: Synthesis and NMR conformational investigation

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