Abstract
Anions of nitroderivatives of thiophene and furan were subjected to the reactions with selected C-H acids in the gas phase. Various structures and reaction pathways were proposed for the observed ionic products. In general, the reactions of heteroaromatic anions with C-H acids may be divided into three groups, depending on the proton affinity difference between C-H acid’s conjugate base and heteroaromatic anion (ΔPA). The proton transfer from C-H acid to heteroaromatic anion is a dominant process in the reactions for which ΔPA < 0 kcal mol−1, whereas the reactions with high ΔPA (ΔPA > 16 kcal mol−1) do not lead to any ionic products. The formation of σ-adducts and products of their further transformations according to the VNS, SNAr, cine, and tele substitution mechanisms have been proposed for reactions with moderate ΔPA. The other possible mechanisms as SN2 reaction, nucleophilic addition to the cyano group, ring-opening pathway, and halogenophilic reaction have also been discussed to contribute in the reactions between heteroaromatic anions and C-H acids. Graphical ᅟ Electronic supplementary materialThe online version of this article (doi:10.1007/s13361-015-1122-1) contains supplementary material, which is available to authorized users.
Highlights
Anionic σ-adducts (often referred to as JacksonMeisenheimer or Meisenheimer complexes) are formed as the result of addition of a nucleophile to electrophilic aromatic ring
Anionic σ-adducts are formed as the result of addition of a nucleophile to electrophilic aromatic ring
In the first series of experiments, we examined the generation of selected nitroheteroaromatic anions from the appropriately substituted carboxylate anions via decarboxylation and their gas-phase stability, which in turn is highly required for further investigation of their ion-molecule reactions
Summary
Anionic σ-adducts (often referred to as JacksonMeisenheimer or Meisenheimer complexes) are formed as the result of addition of a nucleophile to electrophilic aromatic ring. Reaction of 2-nitrothiophene 5-anion with chloroacetonitrile and methyl chloroacetate according to proton transfer followed by σH-adduct formation and elimination of HCl typically about 18 kcal mol−1 [38, 39], formation of adducts was mainly observed.
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