Effects of chemical substitution upon excited state proton transfer. Fluoroderivatives of salicylaldimine

Forés, Marta; Scheiner, Steve

doi:10.1016/s0301-0104(99)00179-2

Cited by 37 publications

(14 citation statements)

References 54 publications

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“…Determination of the energy of the intramolecular hydrogen bond is a difficult task experimentally, so to settle this problem ab initio and semi-empirical methods of calculations were used [136][137][138][139][140][141][142][143][144][145][146][147] for Schiff bases. [141][142][143][144][145][146][147] However, there the question arises of how to define a reference state, the most stable one among the states deprived of a hydrogen bond.…”

Section: Conformers In Ground Statementioning

confidence: 99%

“…137 and references cited therein). Scheiner and co-workers 138,139 put forward the suggestion of employing a conformer with the hydroxyl group turned by 180 around the carbonyl bond in ortho-substituted phenols. A similar suggestion was made for N-methylsalicylaldimine (R 1 ¼ H, R 2 ¼ CH 3 , R 3 ¼ H) on the basis of semi-empirical CNDO/2 calculations 142 (conformer 6 in Scheme 8).…”

Section: Conformers In Ground Statementioning

confidence: 99%

“…However, this suggestion was called in to question in several studies 75,139,140,144 where a series of conformers of aldimines and Mannich bases were calculated with application of semi-empirical (AM1, PM3) and ab initio [HF/3-21G, B3LYP/6-31(d,p), MP2/6-31(d,p), B3LYP/ d-95(d,p)] methods. The results obtained indicate that the most stable non-hydrogen-bonded conformer is that with both groups turned by 180 (conformer 3).…”

Section: Conformers In Ground Statementioning

confidence: 99%

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Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Filarowski

2005

J of Physical Organic Chem

122

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This review deals with selected aspects of research on o-hydroxyaryl Schiff bases. Special attention is given to results obtained by x-ray, IR, UV and NMR spectroscopic methods and quantum-mechanical calculations that allow a better understanding of the nature of o-hydroxyaryl Schiff bases. The paper reports on studies of sterically modified o-hydroxyaryl Schiff bases with an intramolecular hydrogen bond made short owing to steric repulsion. The following points are focused upon: structural and energetic analysis of the steric effect and its influence on the hydrogen bond length; proton localization and the proton transfer process; the impact of proton transfer on the chelate and phenol rings in the intramolecular hydrogen bond; a generalized scheme of tautomer equilibrium and its study with the use of experimental and theoretical methods; some discrepancies found in standard parameters for a particular tautomeric form; calculations of the potential energy curve for basic tautomer forms; influence of the steric effect on the potential curve shape; and a review of semi-empirical and quantum-mechanical calculations of molecular structures in the ground state.

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Section: Conformers In Ground Statementioning

confidence: 99%

Section: Conformers In Ground Statementioning

confidence: 99%

Section: Conformers In Ground Statementioning

confidence: 99%

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Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Filarowski

2005

J of Physical Organic Chem

122

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“…Their unusual stabilization energy makes them to be distinguished from ordinary hydrogen bonds. All cases of strong and very strong hydrogen bonds have been classified into charge assisted hydrogen bond (CAHB) and resonance assisted hydrogen bond (RAHB) [13] which have been widely studied [14][15][16][17][18][19][20][21][22][23]. The enhancement of hydrogen bonding energy by additional factors, as the polarity of the donor and acceptor groups, can lead to proton transfer between molecules with formation of a salt.…”

Section: Introductionmentioning

confidence: 99%

Co-crystal/salt crystal structure disorder of trichloroacetic acid–N-methylurea complex with double system of homo- and heteronuclear O–H···O/N–H···O hydrogen bonds: X-ray investigation, ab initio and DFT studies

Rybarczyk‐Pirek

2012

Struct Chem

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The X-ray diffraction studies revealed disorder of a trichloroacetic acid-N-methylurea complex crystal structure, connected with a proton transfer via O-HÁÁÁO hydrogen bond. The observed structure corresponds to a co-existence of ionic (salt) and neutral (co-crystal) forms of the complex in the solid state in ratio 3:1, respectively. The geometrical analysis based on ab initio and density functional theory methods combined with the experimental research indicated that two different N-methylurea molecular conformations, defined by CNCN torsion angle, correspond to the neutral and the ionic form of the complex, respectively. The conformational changes seem to be connected with stabilization of the ionic structure after a proton transfer, as according to theoretical calculations this form of the complex (the ionic one) was unstable in the gas phase. A particular attention was focused on a system of a double intermolecular hydrogen bonds, O-HÁÁÁO and N-HÁÁÁO which join molecules into the title complex. The analysis of these interactions performed in terms of their geometry, energetic and topological electron density properties let for their classification into strong and medium strength hydrogen bonds. It was also found that the antibonding hydrogen bonding donor orbital occupation corresponded to the stabilization energy resulting from charge transfer in hydrogen bonds. Hence, it is postulated as a possible indicator of interaction strength.

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“…Moreover, the fluorescence emission intensities depend upon the introduction of different substitutions in the ligand molecules. Electron‐donating groups and electron‐withdrawing groups on the 6/8‐position of the coumarin ring can drastically alter the electron density and the electron conjugate system of the ligands A n 33, 34. However, when the heterochelates are excited at the same wavelength, the spectra of the heterochelates [Cu(A n )(CQ)(OH)] • x H 2 O (where n = 1–4 and x = 3, 2, 4, 1) have a slightly red shift as compared with the ligands as shown in Fig.…”

Section: Resultsmentioning

confidence: 99%