Reactivity of <i>trans</i>- and <i>cis</i>-Phenyldiazene Induced by the Internal Rotation of the Phenyl Group

Zevallos, Jenny; Letelier, Jorge Ricardo; Toro-Labbé, Alejandro

doi:10.1021/jp040321n

Cited by 8 publications

(10 citation statements)

References 40 publications

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“…Internal rotation of the phenyl group induces the reactivity in trans - and cis -phenyldiazene. For both isomers, the planar conformers are the most electrophilic and transition states are the least electrophilic (the cis-isomer has a maximum ω value in one of the TSs), which accounts for the extra electronic delocalization in the transition states . This unexpected behavior may be rationalized 338 by the fact that both μ and η are maxima at the TS.…”

Section: 2 Molecular Internal Rotationsmentioning

confidence: 94%

Electrophilicity Index

2006

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Section: 2 Molecular Internal Rotationsmentioning

confidence: 94%

Electrophilicity Index

2006

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“…The nucleophilic Fukui functions condensed to atoms (Fukui indexes) were obtained through a modified version of Gaussian 03 (14). A high value of the Fukui indexes on a given atom k indicates a high probability that protonation occurs on that center (17,18).…”

Section: Methodsmentioning

confidence: 99%

Structure and Medium Effects on the Photochemical Behavior of Nonfluorinated Quinolone Antibiotics†

Pavez

Herrera

Toro–Labbé

et al. 2007

Photochemistry and Photobiology

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The photophysical behavior of the quinolone antibiotics, oxolinic (OX), cinoxacin (CNX) and pipemidic (PM) acids was studied as a function of pH and solvent properties. The ground state of these compounds exhibits different protonated forms, which also exist in the first excited states. Theoretical calculations of the Fukui indexes allowed to assigning the different protonation equilibria. The pK values indicate that the acidity of the 3-carboxylic and 4-carbonyl groups increases with the N-atom at position 2 in CNX. It has been found that fluorescence properties are strongly affected by pH, the more fluorescent species is that with protonated carboxylic acid, protonated species at the carbonyl group and the totally deprotonated form present very low fluorescence. The fluorescence behavior also depends on the chemical structure of the quinolone and on the solvent properties. The analysis of the solvent effect on the maximum and the width of the fluorescence band of OX, using the linear solvent-energy relation solvatochromic equation, indicates that the polarizability and hydrogen bond donor ability are the parameters that condition the spectral changes. The hydrogen bond acceptor ability of the solvents also contributes to the spectral shifts of CNX. The compound bearing the piperazinyl group at the position 7, PM only is fluorescent in high protic solvents. These results are discussed in terms of the competition between the intra- and intermolecular hydrogen bonds. The irradiation of OX, CNX and PM using 300 nm UV light led to a very low photodecomposition rate. Under the same conditions the nalidixic acid (NA), a structurally related quinolone, photodecomposes two orders of magnitude faster.

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“…The Fukui indexesfk for different protonated forms of NA were calculated using the following formula fk = $h(r)/2dr, where I@(r)I2 is the electronic density associated to the highest occupied molecular orbital (26,27), and the integration is performed within the space that defines atom k. Figure 3 shows bar charts representing the Fukui function f;…”

Section: Theoretical Calculationsmentioning

confidence: 99%

Photophysics and Photochemistry of Nalidixic Acid†

Pavez

Toro–Labbé

Encinas

2006

Photochem Photobiol

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The photophysics and photochemistry of nalidixic acid (NA) were studied as function of pH and solvent properties. The ground state of NA exhibits different protonated forms in the range of pH 1.8-10.0. Fluorescence studies showed that the same species exist at the lowest singlet excited state. Absorption experiments were carried out with NA and with the methylated analog of nalidixic acid (MNE) in different organic solvents and water pH 3, where the main species corresponds to that protonated at the carboxylic group. These studies and the DFT calculation of torsional potential energy profiles suggest that the most stable conformation of the NA in nonprotic solvents corresponds to a closed structure caused by the existence of intramolecular hydrogen bond. Absorption and fluorescence spectra were studied in sulfuric acid solution. The pK value (Ho -1.0) found in these conditions was attributed to the protonation of the 4' keto oxygen atom of the heterocyclic ring. Theoretical calculations (DFT/B3LYP/6-311G*) of the energies of the different monoprotonated forms of the NA and Fukui indexes (f(x)-) showed that the species with the proton attached to 4' keto oxygen atom is the most stable of all the cationic forms. MNE and enoxacin also showed the protonation of the 4' keto oxygen atom with similar pK values. The photodecomposition of NA is dependent on the medium properties. Faster decomposition rates were obtained in strong acid solution. In nonprotic solvents, a very slow decomposition rate was observed.

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Reactivity of trans- and cis-Phenyldiazene Induced by the Internal Rotation of the Phenyl Group

Cited by 8 publications

References 40 publications

Electrophilicity Index

Electrophilicity Index

Structure and Medium Effects on the Photochemical Behavior of Nonfluorinated Quinolone Antibiotics†

Photophysics and Photochemistry of Nalidixic Acid†

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