Effet de cation sur la réactivité ambidente des anions: la nette tendance à la O-alkylation manifestée par les énolates de lithium de composés β-dicarbonylés

1980 ◽  
Vol 58 (8) ◽  
pp. 786-793 ◽  
Author(s):  
P. Sarthou ◽  
G. Bram ◽  
F. Guibe
Keyword(s):  
Ion Pairs ◽  
Lithium Ion ◽  
Intrinsic Property ◽  
Alkyl Halides ◽  
Alkyl Sulfonates ◽  
Lithium Enolates ◽  
Leaving Group ◽  
Nucleophilic Reactivity ◽  
Specific Reactivity ◽  
Marked Tendency

The study of the specific reactivity of the ion pairs of alkaline enolates of β-dicarbonyl compounds shows that the lithium enolates, in spite of their characteristically strong enolate–cation interactions display, especially when compared to sodium enolates, a marked tendency towards O-alkylation. This strong O-/C-nucleophilicity of the lithium ion pairs is not very sensitive to changes in medium polarity (from THF or DME to DMF) but depends on the nature of the alkylating agent, being enhanced with moderately electrophilic alkyl sulfonates or sulfate but lessened with alkyl halides or with very electrophilic sulfonates (triflate). It is suggested that the lithium enolate tendency towards O-alkylation is partly the result of a Li+ – leaving group interaction (especially in the case of the sulfonates) and partly an intrinsic property of the enolate–lithium ion pair; this latter property is discussed in terms of the respective solvation abilities towards cations of the C- and O-alkylation transition states.Some of our results about the nucleophilic reactivity of ion pairs in DMF are at variance with previous reports in the literature. The origin of the discrepancy is discussed.

Use of Tetrachlorophthalimide for Identification of Alkyl Halides and Alkyl Sulfonates.

1965 ◽  
Vol 37 (1) ◽  
pp. 158-159 ◽  
Author(s):  
C. F. H. Allen ◽  
W. R. Adams ◽  
C. L. Myers
Keyword(s):  
Alkyl Halides ◽  
Alkyl Sulfonates

scholarly journals Synergistic Effect of a Defect-Free Graphene Nanostructure as an Anode Material for Lithium Ion Batteries

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 9 ◽  
Author(s):  
Kwang Hyun Park ◽  
Byung Gon Kim ◽  
Sung Ho Song
Keyword(s):  
Graphene Oxide ◽  
Lithium Ion Batteries ◽  
Anode Material ◽  
Graphene Nanosheets ◽  
Rate Capability ◽  
Intercalation Compound ◽  
Lithium Ion ◽  
Intrinsic Property ◽  
Power Performance ◽  
Graphene Nanostructure

Graphene nanosheets have been among the most promising candidates for a high-performance anode material to replace graphite in lithium ion batteries (LIBs). Studies in this area have mainly focused on nanostructured electrodes synthesized by graphene oxide (GO) or reduced graphene oxide (rGO) and surface modifications by a chemical treatment. Herein, we propose a cost-effective and reliable route for generating a defect-free, nanoporous graphene nanostructure (df-GNS) through the sequential insertion of pyridine into a potassium graphite intercalation compound (K-GIC). The as-prepared df-GNS preserves the intrinsic property of graphene without any crystal damage, leading to micro-/nano-porosity (microporosity: ~10–50 µm, nanoporosity: ~2–20 nm) with a significantly large specific surface area. The electrochemical performance of the df-GNS as an anode electrode was assessed and showed a notably enhanced capacity, rate capability, and cycle stability, without fading in capacity or decaying. This is because of the optimal porosity, with perfect preservation of the graphene crystal, allowing faster ion access and a high amount of electron pathways onto the electrode. Therefore, our work will be very helpful for the development of anode and cathode electrodes with higher energy and power performance requirements.

Ambident Heterocyclic Reactivity: Alkylation of 4-Substituted and 2,4-Disubstituted Benzimidazoles

1994 ◽  
Vol 47 (8) ◽  
pp. 1523 ◽  
Author(s):  
MR Haque ◽  
M Rasmussen
Keyword(s):  
Hydrogen Bonding ◽  
Transition State ◽  
Electrostatic Field ◽  
Transition States ◽  
Alkyl Halides ◽  
Methyl Group ◽  
Site Selectivity ◽  
Leaving Group ◽  
Standard Set ◽  
Specific Association

The N1/N3-alkylation patterns of 4-amino-, 4-methyl- and 4-nitro-benzimidazole anions, and their 2-methyl analogues, with a standard set of primary alkyl halides (in dimethylformamide, 30°) have been determined and compared. The observed regioselectivities are dominated by proximal effects-electrostatic field, non-bonded steric and in some cases specific association (hydrogen bonding)-the interplay of which is critically dependent on the (variable) geometries of the SN2 transition states involved, in particular on the N---C distance of the developing N-alkyl bonds. The presence of a symmetrically placed 2-methyl group produces an enhanced N1/N3 site selectivity, very sensitive to the loose-tight nature of the transition state. Halide leaving group effects on butylation regioselectivities of 2-unsubstituted, 2-ethoxy-, 2-methyl- and 2-chloro-4-methylbenzimidazole anions, whilst small, are consistent with a Bell-Evans-Polanyi analysis of SN2 transition state variations, with the earlier transition states of CH3(CH2)3I leading to reduced regioselectivities.

Regio- and Stereoselective (SN2) N-, O-, C- and S-Alkylation using Trialkyl Phosphates

Synthesis ◽  
2021 ◽  
Author(s):  
Amit banerjee ◽  
Tomohiro Hattori ◽  
Hisashi Yamamoto
Keyword(s):  
Room Temperature ◽  
Alkylating Agents ◽  
Alkyl Halides ◽  
Back Side ◽  
Alkyl Groups ◽  
Wide Range ◽  
Leaving Group ◽  
Reaction Proceeds ◽  
Trialkyl Phosphates ◽  
Trialkyl Phosphate

Bimolecular nucleophilic substitution (S N 2) is one of the most known fundamental reactions in organic chemistry to generate new molecules from two molecules. In principle, a nucleophile attacks from the back side of an alkylating agent having a suitable leaving group, most commonly using a halide. However, alkyl halides are expensive, very harmful, toxic and not so stable which makes them problematic for laboratory use. In contrast, trialkyl phosphates are cheap, readily accessible, stable at room temperature, under air, and are easy to handle but rarely used as alkylating agents in organic synthesis. Here, we describe a mild, straightforward and powerful method for nucleophilic alkylation of various nucleophiles such as N-, O-, C- and S- using readily available trialkyl phosphate. The reaction proceeds smoothly with excellent yield and quantitative yield in many cases and covers a wide range of substrates. Further, the rare stereoselective transfer of secondary alkyl groups has been achieved with inversion of configuration of chiral centers (up to >99% ee).

A Raman spectral study of solvation and ion association in the systems LiAsF6/CH3CO2CH3 and LiAsF6/HCO2CH3

1991 ◽  
Vol 69 (11) ◽  
pp. 1766-1773 ◽  
Author(s):  
Zhongyi Deng ◽  
Donald E. Irish
Keyword(s):  
Methyl Acetate ◽  
Methyl Formate ◽  
Ion Pairs ◽  
Lithium Ion ◽  
Ion Association ◽  
Ion Solvation ◽  
Lithium Cation ◽  
Different Types ◽  
Raman Spectral ◽  
Contact Ion Pairs

The structure of the solvated lithium cation in methyl acetate (MA) solutions has been investigated using Raman spectroscopy. Two bands at 844 and 864 cm−1 have been assigned to two different types of MA: the former is from the bulk solvent and the latter arises from MA molecules solvating the lithium cation. From measurement of changes in intensity of these bands with increasing salt concentration a solvation number of four for Li+ in MA has been inferred. Changes in the Raman bands at ca. 1740 cm−1 suggest that solvation occurs through the carbonyl group. Evidence for contact ion pairing between Li+ and AsF6− is also presented. An equilibrium between solvent-shared ion pairs and contact ion pairs is proposed for which an equilibrium constant is estimated. The system LiAsF6/methyl formate (MF) is similar in structure. Key words: Raman, ion pair formation, lithium and hexafluoroarsenate ions, methyl acetate and formate, lithium ion solvation.

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