Regioselectivity of Pyridine Deprotonation in the Gas Phase

Schafman, Bonnie; Wenthold, Paul G.

doi:10.1021/jo062117x

Cited by 27 publications

(41 citation statements)

References 60 publications

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“…Moreover, Yamamoto has reported that 2,5‐dibromo‐6‐hexylpyridine also afforded only 5‐chloromagnesio pyridine in the reaction with i PrMgCl 7. These results can be accounted for by the fact that the chloromagenesio group at the 2‐position would suffer repulsion from the lone pair of the nitrogen of the pyridine ring 17. In the reaction of 1 with i PrMgCl, however, coordination of the oxygen of the MEEO group to magnesium would promote the bromo‐chloromagnesio exchange reaction at the 2‐position to some extent, to afford 2‐chloromagnesiopyridine 7 as a minor product 18…”

Section: Resultsmentioning

confidence: 99%

“…7 These results can be accounted for by the fact that the chloromagenesio group at the 2-position would suffer repulsion from the lone pair of the nitrogen of the pyridine ring. 17 In the reaction of 1 with i PrMgCl, however, coordination of the oxygen of the MEEO group to magnesium would promote the bromo-chloromagnesio exchange reaction at the 2-position to some extent, to afford 2-chloromagnesiopyridine 7 as a minor product. 18 Polymerization and Polymer Structure Polymerization of Grignard monomer 6 and 7, generated from 1 with i PrMgCl, was carried out by addition of 1.8 mol % Ni(dppp)Cl 2 to the reaction mixture, as in the case of the polymerization of Grignard alkylthiophene monomers, 2 but a yellow solid was unexpectedly precipitated within 1 h. The polymerization, however, was continued for 3 h (Scheme 3).…”

Section: Synthesis Of Monomer Precursor and Generation Of Grignard-tymentioning

confidence: 99%

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Synthesis of novel blue‐light‐emitting polypyridine

Nanashima

Yokoyama

Yokozawa

2012

J. Polym. Sci. A Polym. Chem.

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A new regioregular head‐to‐tail (HT)‐type polypyridine with methoxyethoxyethoxy (MEEO) side chains, HT‐PMEEOPy, was synthesized by means of Kumada‐Tamao coupling polymerization of a Grignard monomer with a Ni catalyst. Although the polymer was precipitated in THF during polymerization, multiangle laser light scattering (MALLS) analysis indicated that the weight‐average molecular weight (Mw) was about 25,000. The HT content in the polymer was 95%. A solution of HT‐PMEEOPy in CHCl3 was found to emit a strong blue light when the solution was irradiated with UV light; the UV‐vis absorption maximum (λmax) and photoluminescence maximum (λmax em) were at 392 and 460 nm, respectively. To clarify the effect of regioregularity of PMEEOPy on the photoluminescence, head‐to‐head (HH) PMEEOPy was synthesized by means of Yamamoto coupling polymerization. The photoluminescence of HH‐PMEEOPy (λmax = 330 nm, λmax em = 414 nm) was weaker than that of HT‐PMEEOPy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

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Section: Resultsmentioning

confidence: 99%

Section: Synthesis Of Monomer Precursor and Generation Of Grignard-tymentioning

confidence: 99%

Synthesis of novel blue‐light‐emitting polypyridine

Nanashima

Yokoyama

Yokozawa

2012

J. Polym. Sci. A Polym. Chem.

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“…To further explore the substituent effect of the N-oxide in the ring, we have turned to an analysis developed by Schafman and Wenthold 11. Using the established relationship between resonance and field effects determined by Taft for benzoic acids in the gas phase (Equations 1 and 2), it is possible to extract pseudo-Hammett parameters for the ring N-oxide 20.…”

Section: Discussionmentioning

confidence: 99%

“…Deprotonated pyridine has an experimental PA of 389.9 kcal/mol11 and therefore oxidation decreases the ΔH acid of pyridine by about 10 kcal/mol. Schafman and Wenthold have analyzed positional acidities in pyridine in detail and has found that the para position is slightly more acidic than the meta position, and both are much more acidic than the ortho position11. To allow for a fair comparison, we have recomputed the positional acidities of pyridine at the G3MP2 level (Table 1, Scheme 2) and the values are consistent with Wenthold’s work.…”

Section: Discussionmentioning

confidence: 99%

The Stability of Aryl Carbanions Derived from PyridineN-Oxide: The Role of Resonance in Stabilizing Aryl Anions

et al. 2009

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The gas phase stability of carbanions centered at various positions on pyridine N-oxide were investigated by computational and experimental methods. In addition, G3MP2 computations were completed on ring-deprotonated pyridine and N-methylpyridinium. With these species, the effect of a nitrogen-centered positive charge on carbanion stability was assessed. Introduction of the nitrogenoxide group into the benzene ring decreases the ΔH acid by about 20 kcal/mol, but surprisingly, the effect is nearly independent of the position of the group (ortho, meta, or para). The results indicate that the N-oxide offers a balance of field, resonance, and local effects that cancels out any positional preferences. G3MP2 calculations indicate that a similar lack of positional selectivity is seen in nitrobenzene and benzonitrile. Overall, the data suggest that π-effects are limited in phenyl anions and as a result, ylide-like, rather than carbene-like, resonance structures are most important in the anions derived from ring deprotonation of arenes and heterocycles of these general types.

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“…It must be mentioned, however, that one of the main drawbacks of the proton abstraction method is its poor selectivity when there is more than one deprotonation site with comparable acidity in the molecule. For example, Schafman and Wenthold (2007) showed that in the gas-phase reaction of pyridine with OH À ion, 3-and 4-pyridide ions are formed in an approximately 1:4 ratio. Therefore, the deprotonation method gives information about the thermodynamics of the carbanion formation reactions, which makes it very useful, for example, in proton affinity (PA) measurements.…”

Section: Proton Transfer Reactionsmentioning

confidence: 99%

Negative ion gas‐phase chemistry of arenes

Danikiewicz

Zimnicka

2015

Mass Spectrometry Reviews

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Reactions of aromatic and heteroaromatic compounds involving anions are of great importance in organic synthesis. Some of these reactions have been studied in the gas phase and are occasionally mentioned in reviews devoted to gas-phase negative ion chemistry, but no reviews exist that collect all existing information about these reactions. This work is intended to fill this gap. In the first part of this review, methods for generating arene anions in the gas phase and studying their physicochemical properties and fragmentation reactions are presented. The main topics in this part are as follows: processes in which gas-phase arene anions are formed, measurements and calculations of the proton affinities of arene anions, proton exchange reactions, and fragmentation processes of substituted arene anions, especially phenide ions. The second part is devoted to gas-phase reactions of arene anions. The most important of these are reactions with electrophiles such as carbonyl compounds and α,β-unsaturated carbonyl and related compounds (Michael acceptors). Other reactions including oxidation of arene anions and halogenophilic reactions are also presented. In the last part of the review, reactions of electrophilic arenes with nucleophiles are discussed. The best known of these is the aromatic nucleophilic substitution (SN Ar) reaction; however, other processes that lead to the substitution of a hydrogen atom in the aromatic ring are also very important. Aromatic substrates in these reactions are usually but not always nitroarenes bearing other substituents in the ring. The first step in these reactions is the formation of an anionic σ-adduct, which, depending on the substituents in the aromatic ring and the structure of the attacking nucleophile, is either an intermediate or a transition state in the reaction path. In the present review, we attempted to collect the results of both experimental and computational studies of the aforementioned reactions conducted since the very beginning of gas-phase negative ion chemistry.

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Regioselectivity of Pyridine Deprotonation in the Gas Phase

Cited by 27 publications

References 60 publications

Synthesis of novel blue‐light‐emitting polypyridine

Synthesis of novel blue‐light‐emitting polypyridine

The Stability of Aryl Carbanions Derived from PyridineN-Oxide: The Role of Resonance in Stabilizing Aryl Anions

Negative ion gas‐phase chemistry of arenes

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