The Quantitative Treatment of the Ortho Effect

Charton, Marvin

doi:10.1002/9780470171875.ch3

Cited by 130 publications

(13 citation statements)

References 129 publications

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“…Spectroscopic Measurements and General Considerations. 1 H and 13 C NMR spectra were recorded on a Bruker DPX-250 (250 MHz) spectrometer with the solvent residual peaks as the internal standard (Scientific and Educational Laboratory of Resonance The instrument was operated in positive mode using an m/z range of 50−1200. The capillary voltage of the ion source was set at 4000 V. The nebulizer gas pressure was 1.0 bar, and the drying gas flow was set to 4.0 L/min.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…1 H NMR (400 MHz, CDCl 3 ): δ = 7.34 (d, J = 7.8 Hz, 1 H), 7.17 (d, J = 7.8 Hz, 1 H), 6.81 (d, J = 7.8 Hz, 2 H), 5.08 (s, 2 H), 2.90 (s, 3 H), 2.83 (s, 6 H, NMe 2 ), 2.79 (s, 6 H, NMe 2 ), OH group is not observable. (16), 227 (13), 214 (17), 213 (19), 212 (21), 211 (18), 210 (22), 209 (16), 198 (16), 197 (15), 196 (32), 195 (15), 182 (34), 181 (23), 168 (27), 167 (15), 154 (17), 127 (16), 115 (19) 1,8-Bis(dimethylamino)-4,5-dimethylnaphthalene (B2). Aqueous 37% HBr (1 mL, 6.9 mmol) and 5% Pd−C (0.50 g) were added to a solution of alcohol 7 (1.78 g 6.9 mmol) in methanol (100 mL) and the resulting mixture was agitated in a hydrogen atmosphere for 120 h. After completion of the reaction, the catalyst was filtered off, the solvent was removed, and the remainder was dissolved in aqueous 20% KOH (20 mL).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Three spherically shaped groups were chosen as bulky substituents, Br, Me, and SiMe 3 , whose van der Waals (VdW) radii are equal to 1.95, 2.00, and 3.90 Å, respectively. 13 Within the framework of the task, we considered four types of DMAN derivatives labeled as A−D (for consistency, compounds 1 and 2 have also been assigned alternate numbers A1 and A2, Figure 3).…”

Section: ■ Introductionmentioning

confidence: 99%

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Combination of “Buttressing” and “Clothespin” Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

et al. 2021

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A series of previously unknown 2,4,5-tri-and 2,4,5,7-tetrasubstituted 1,8bis(dimethylamino)naphthalenes and their salts with HBF 4 containing bulky spherically shaped substituents (Me, Br, and SiMe 3 ) in the naphthalene ring has been synthesized. Using XRD analysis of 11 samples, the influence of the so-called "buttressing" and "clothespin" effects on their molecular structure and the NHN hydrogen bond geometry in the solid cations were investigated. The combined action of both effects has been shown to significantly increase the compression of the hydrogen bond. As a result, the previous record of the hydrogen bond shortness (N•••N = 2.524 Å) has been surpassed in favor of 2.502 Å found for the tetrafluoroborate of 2,4,5,7-tetramethyl-1,8-bis-(dimethylamino)naphthalene. The molecular structure of the latter differs by perfect symmetry and practically barrier-free proton transfer in the [NHN] + bond. On the basis of the results of quantum-chemical calculations, it is suggested that the value of 2.502 Å likely represents or lies very close to the theoretical limit for the short hydrogen bonds between the amine-type nitrogen atoms.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Combination of “Buttressing” and “Clothespin” Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

et al. 2021

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“…The earlier attempts involved the assumption that polar effects at the ortho position would mirror those at the para position and several examples of the application of this approach have been discussed . Charton has suggested that it is unlikely that σ o scales of wide applicability can be developed . Charton developed a steric parameter (υ), which is based on hydrogen as the standard (υ = o), with the result that all values are positive .…”

Section: Introductionmentioning

confidence: 99%

The importance of the ortho effect in the solvolyses of 2,6‐difluorobenzoyl chloride

Park

Kevill

2011

J of Physical Organic Chem

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The ortho effect of the chloro substituents in 2,6-dichlorobenzoyl chloride sufficiently hindered attack on the acyl carbon such that an ionization mechanism was observed over the full range of solvents studied. We now compare this behavior with that of 2,6-difluorobenzoyl chloride. The smaller fluoro substituents allow the dominant pathway to be addition-elimination (association-dissociation) in all solvents except those rich in fluoroalcohol, where ionization is dominant. Ranges of operation for both mechanisms had previously been observed for the parent benzoyl chloride but with a wider ionization range than for the 2,6-difluoro derivative. This indicates that, relative to the parent, the electronic destabilizing influence of the fluorines on acyl cation formation outweighs the steric retardation to attack because of the presence of the two ortho-fluorine atoms. An extended (two-term) Grunwald-Winstein equation treatment of the solvolyses of 2,6-difluorobenzoyl chloride is reported.

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“…particularities of substrate solvation. This is also the reason why a standard a value cannot be determined for a nitro group in ortho position (33). ferent a2NO2 values depending on solvents and type of reaction.…”

Section: T Should Be Remembered T H a T T H Ementioning

confidence: 99%

Mechanism of Ester Aminolysis in Aprotic Media and Specific Solvent Effects

Nagy

Reuliaux

Bertrand

et al. 1985

Bulletin des Soc Chimique

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The n-butylaminolysis of nitro-substituted 4'-nitrophenyl benzoates and cinnamates as well as of phenylacetates in aprotic solvents is governed by a kinetic law implying higher order terms in nucleophile. It is shown that the attacking nucleophile forms a n-a type molecular complex with the substrate before reaching the transition state in the subsequent kinetic step. This molecular complex is a true reaction intermediate as evidenced by the observed negative activation enthalpy. Othernlecules intervene as general base catalysts. Tertiary m i n e d also c a t a l y s 3 h e reaction. Their catalytic activity i s linearly related to their hydrogen bond forming ability and it is not a direct function of their proton basicity. By varying the nucleophile structure, an excellent BrOnsted relationship could be obtained for the first time in aprotic media, the 6 of which confirms that the catalytic collapse of tetrahedral intermediate is the rate determining step. The reaction of cinnamates turns out to be less sensitive to structural changes of th. substrate than is the reaction of benzoates as shown by the corresponding Hammetovalues. The electronic effects of 2-nitro groups are strongly solvent dependent. Once more, it is established that &enever specific solvent effects (n-donor or ndonor ability) are present, they dominate the overall effect. A general reaction mechanism is proposed which not only explains the various roles played by the nucleophile but also accounts successfully for the great variety of kinetic schemes observed in aprotic media. Transacylation reactions are very important in chemistry and biology.Therefore, the study and elucidation of their mechanism present a considerable interest. well understood(2) while a number of well established facts are known in aprotic solvents(3). It seems to be general in aprotic solvents that higher order terms in nucleophile appear in the kinetic eq~ation(~"'~) implying a general base catalysisi this catalytic effect can also be shown by unhindered tertiary a m i n e~(~) r the existence of tetrahedral intermediate is not definitely established but, if it exists, its collapse leading to products can ba considered as rate deter~uining'~).In the present paper, we attempt to elucidate further the mechanism of ester aminolysis reactions. We also show the influence of structural and solvent effects on this mechanism.A series of nitro-substituted benzoates, cinnamateb and acetates has been submitted to n-butylaminolysis in various aprotic solvents (Table 1). The solvents have been chosen in such a way as to represent both general (polarity, The mechanism of ester aminolysis reactions in aqueous media is fairly -1055 -

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The Quantitative Treatment of the Ortho Effect

Cited by 130 publications

References 129 publications

Combination of “Buttressing” and “Clothespin” Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

Combination of “Buttressing” and “Clothespin” Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

The importance of the ortho effect in the solvolyses of 2,6‐difluorobenzoyl chloride

Mechanism of Ester Aminolysis in Aprotic Media and Specific Solvent Effects

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