Theoretical Study of Additivity of the Deprotonation Energies in Aromatics. I. Disubstituted Benzenes

Maksić, Zvonimir B.; Kovaček, Damir; Eckert‐Maksić, Mirjana; Zrinski, Irena

doi:10.1021/jo960376o

Cited by 19 publications

(17 citation statements)

References 9 publications

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“…In particular, we intended to scrutinize the validity of the Maksić approach [13] in this context. This formalism extracts atom-or group-specific increments from a comparison of the computed proton affinities of ortho-, meta-, and para-substituted phenyl anions with that of the parent benzenide itself.…”

Section: Discussionmentioning

confidence: 99%

“…A close numerical agreement is taken as evidence for the additivity of the substituent effects under inspection. [13] If we apply these criteria, we have to rule that both halogens, fluorine as well as chlorine, exhibit additivity of their substituent effects. The increment-derived protonation enthalpies deviate from the directly computed ones by 0.4 kcal mol À1 in the fluoro series and by 1.5 kcal mol À1 in the chloro series.…”

Section: Discussionmentioning

confidence: 99%

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The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

Hyla‐Kryspin¹,

Büker²,

Nibbering³

et al. 2005

Chemistry A European J

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The deprotonation energies of benzene, fluorobenzene, all di-, tri-, and tetrafluorobenzenes, pentafluorobenzene, chlorobenzene, all di-, tri-, and tetrachlorobenzenes, and pentachlorobenzene have been calculated at various levels of second-order Moller-Plesset and density functional theory. Taking the previously determined experimental data as a benchmark, good agreement was achieved in the chloro series even with moderate computational effort, whereas more extended basis sets have to be used to obtain meaningful numbers in the fluoro series. Apparently, most extensive electron correlation is required to avoid artifacts caused by the proximity of nonbonding lone pairs at the carbanionic center and at the fluorine atoms. When two or more fluorine substituents were introduced in the same aromatic ring, their individual effects (as defined by position-dependent acidity increments) proved to be perfectly additive in the entire series. In contrast, the acidifying effect of chloro substituents was found to level off when the number of such halogens increases. Additivity or non-additivity of element effects cannot be ascertained after having merely compared the acidity of mono- and disubstituted substrates, but only after having moved to higher degrees of substitution.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

Hyla‐Kryspin¹,

Büker²,

Nibbering³

et al. 2005

Chemistry A European J

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“…A more efficient and economical alternative, with a fairly small sacrifice in accuracy, is represented by a simplified G2(MP2) procedure. [31] However, we would also like to examine an even simpler theoretical model provided by the MP2(fc)/6-311ϩG**//HF/6-31ϩG* (abbreviated as MP2) computational strategy, [21] which would be more practical than G2(MP2) procedure. It consists of the HF/6-31ϩG* optimization of the molecular structures and the MP2(fc)/6-311ϩG** estimates of the total molecular electron energies obtained by the single-point calculations.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…[20] Furthermore, it is also worth mentioning that substituent effects in aromatics appear to follow an interesting and surprisingly simple additivity rule, [21Ϫ25] which determines the CϪH acidity of the aromatic ring in polysubstituted compounds. It is based on the independent substituent approximation (ISA) model, [21] in which each substituent behaves as if all the others were non-existent. This feature parallels the basicities of polysubstituted aromatic bases [26,27] and facilitates interpretation of acidity in heavily substituted aromatic compounds, which are not easily understood otherwise.…”

Section: Introductionmentioning

confidence: 99%

“…Last but not least, we would like to test the additivity rule in polysubstituted benzenes incorporating the groups described above. It would appear that the additivity rule [21] and trichotomy formula [19] provide powerful means for interpretation of the acidities of polysubstituted benzenes in general, thus placing this study in a wider perspective.…”

Section: Introductionmentioning

confidence: 99%

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Acidity of Substituted Benzenes − An Ab Initio Study of the Influence of Methoxy, Trifluoromethyl and Trifluoromethoxy Groups by a Novel Trichotomy Formula

Kovačević¹,

Maksić²,

Primorac³

2003

Eur J Org Chem

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Keywords: Acidity / Aromaticity / Electrostatic field effect / Substituent effectsThe acidities of mono-and polysubstituted benzenes incorporating one, two, or three OCH 3 , OCF 3 , or CF 3 groups were investigated by use of reliable ab initio theoretical models. The calculated deprotonation energies are in very good agreement with available experimental data, although these are unfortunately sparse. A recently developed novel trichotomy formula proved useful for interpretation of predicted variation in acidity in the monosubstituted compounds. In particular, the long-range final state effect in OCF 3 and CF 3 derivatives is confirmed. It is reflected in the stabilization of the lone-pair electrons formed upon deprotonation at the meta and para positions. The theoretically established long-

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The Acidity of Chloro-Substituted Benzenes: A Comparison of Gas Phase, Ab Initio, and Kinetic Data

et al. 2001

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The deprotonation energies of benzene, chlorobenzene, all di-, tri-, tetrachlorobenzenes, and pentachlorobenzene have been determined in the gas phase using a Fourier transform ion cyclotron resonance mass spectrometer. The values measured differ only slightly, though significantly, from the corresponding data for oligofluorobenzenes. The heavier halogen acidifies orthopositions slightly less and meta-positions slightly more than fluorine does. Moreover, the contributions of three or more chloro substituents are not perfectly additive. In fact the accumulation attenuates the contributions somewhat. Quantum chemical calculations at the MP2/6-311+G* level reproduce the gas-phase acidities fairly well, but reveal special effects when extended to experimentally not observable benzenides carrying the halogens at anion-remote positions. Competition experiments have been performed to assess the relative reactivity of nine oligochlorobenzenes towards sec-butyllithium in tetrahydrofuran at -100 degrees C. An almost exact linear correlation between logarithmic rates and gas-phase acidities has been found.

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Theoretical Study of Additivity of the Deprotonation Energies in Aromatics. I. Disubstituted Benzenes

Cited by 19 publications

References 9 publications

The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

Acidity of Substituted Benzenes − An Ab Initio Study of the Influence of Methoxy, Trifluoromethyl and Trifluoromethoxy Groups by a Novel Trichotomy Formula

The Acidity of Chloro-Substituted Benzenes: A Comparison of Gas Phase, Ab Initio, and Kinetic Data

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