Advanced Organic Chemistry

Carey, Francis A.; Sundberg, Richard J.

doi:10.1007/978-1-4615-8885-6

Cited by 93 publications

(130 citation statements)

References 34 publications

(99 reference statements)

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“…This form is the most stable one in the gas-phase as well as in solution [1–6, 44]. The percentage contents of the imine tautomers ( 2 - 4 ) in the tautomeric mixture are exceptionally small (< 10 -15 %), and from a physicochemical point of view they may be neglected.…”

Section: Relative Stabilitiesmentioning

confidence: 99%

“…For the C-sp 3 atom, which takes the moving proton (C2/C6-sp 3 in 2 / 3 and C4-sp 3 in 4 ), its charge becomes more negative. This increase of the negative charge at ortho - and para - position may partially explain the mechanisms of electrophilic substitutions of aniline [6, 7] and possible participation of the imine forms as intermediates. When proceeding from the neutral form to the radical cation, the negative charge of the C-sp 3 atom additionally augments.…”

Section: Relative Stabilitiesmentioning

confidence: 99%

“…The proton transfer from the exo -amine group to the endo -carbon atom destroys the aromaticity of the ring and strongly destabilizes the imine forms ( 2 - 4 ) in comparison to the enamine one. Usually, the imine tautomers are neglected for aniline [6]. However, investigations of many important biological transformations showed that the energetically less stable tautomer for the neutral form, with particular acid-base, electrophilic-nucleophilic, redox, or even just geometric properties, is often an active intermediate and dictates the mechanism and the product formed.…”

Section: Introductionmentioning

confidence: 99%

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Consequence of one-electron oxidation and one-electron reduction for aniline

2011

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Quantum-chemical calculations were performed for all possible isomers of neutral aniline and its redox forms, and intramolecular proton-transfer (prototropy) accompanied by π-electron delocalization was analyzed. One-electron oxidation (PhNH2 – e → [PhNH2]+•) has no important effect on tautomeric preferences. The enamine tautomer is preferred for oxidized aniline similarly as for the neutral molecule. Dramatical changes take place when proceeding from neutral to reduced aniline. One-electron reduction (PhNH2 + e → [PhNH2]-•) favors the imine tautomer. Independently on the state of oxidation, π- and n-electrons are more delocalized for the enamine than imine tautomers. The change of the tautomeric preferences for reduced aniline may partially explain the origin of the CH tautomers for reduced nucleobases (cytosine, adenine, and guanine).

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Section: Relative Stabilitiesmentioning

confidence: 99%

Section: Relative Stabilitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Consequence of one-electron oxidation and one-electron reduction for aniline

2011

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“…In some advanced organic texts one finds, unattributed, the statement that the greater polarity of the C–F bond allows an attraction between nucleophile and carbon, 8,9 an attraction which is presumably considered to exist in the transition state (ts) of step 1 as well. This explanation, with references, is also given as one of several pertinent factors in Miller’s 1968 monograph on aromatic nucleophilic substitution.…”

Section: Introductionmentioning

confidence: 99%

The Element Effect Revisited: Factors Determining Leaving Group Ability in Activated Nucleophilic Aromatic Substitution Reactions

Senger

Cheng

et al. 2012

J. Org. Chem.

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The “element effect” in nucleophilic aromatic substitution reactions (SNAr) is characterized by the leaving group order, F > NO2 > Cl ≈ Br > I, in activated aryl halides. Multiple causes for this result have been proposed. Experimental evidence shows that the element effect order in the reaction of piperidine with 2,4-dinitrophenyl halides in methanol is governed by the differences in enthalpies of activation. Computational studies of the reaction of piperidine and dimethylamine with the same aryl halides using the polarizable continuum model (PCM) for solvation indicate that polar, polarizability, solvation, and negative hyperconjugative effects are all of some importance in producing the element effect in methanol. In addition, a reversal of polarity of the C–X bond from reactant to transition state in the case of ArCl and ArBr compared to ArF also contributes to their difference in reactivity. The polarity reversal, and hyperconjugative influences have received little or no attention in the past. Nor has differential solvation of the different transition states been strongly emphasized. An anionic nucleophile, thiolate, gives very early transition states and negative activation enthalpies with activated aryl halides. The element effect is not established for these reactions. We suggest that the leaving group order in the gas phase will be dependent on the exact combination of nucleophile, leaving group, and substrate framework. The geometry of the SNAr transition state permits useful, qualitative conceptual distinctions to be made between this reaction and other modes of nucleophilic attack.

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“…In support of this hypothesis, use of a more polar solvent, THF, decreased the yield in comparison to 1,2-dichloroethane, a less polar solvent. 23 The best result was obtained when TsOH was used as the catalyst, which gave a 41% yield. Further investigation of this reaction is underway on model systems.…”

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confidence: 99%