Cyano-, Nitro-, and Alkoxycarbonyl-Activated Observable Stable Enols of Carboxylic Acid Amides

Mukhopadhyaya, Jayanta K.; Sklenák, Štěpán; Rappoport, Zvi

doi:10.1021/jo000293e

Cited by 30 publications

(46 citation statements)

References 30 publications

(35 reference statements)

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“…(1) Addition of nucleophiles (e.g., H 2 O, RR′NH) to ketenes;4–14 this mostly gives short‐lived enols,4–14 although several of them are kinetically stabilized by bulky aryl groups15–23 and are sufficiently long‐lived to be detected by 1 H and 13 C NMR spectroscopies 15–23. (2) Addition of organic isocyanates RNCO to CH 2 YY′ (where Y and Y′ are electron‐withdrawing groups (EWGs)) gives the amides 2 , and/or their enols 1 , X = NRR′ or 1 / 2 mixtures 24–32. Many of these enols are thermodynamically stable and many of their solid state structures were determined by X‐ray crystallography.…”

Section: Introductionmentioning

confidence: 99%

The Photoelectric Response of Gold‐Nanoparticle Monolayers

Tang

Rong

et al. 2007

ChemPhysChem

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Self-assembled arrays of metal nanoparticles, due to their novel properties, have been applied to optoelectronic devices, [1][2][3] electronic devices, [4,5] and the enhancement of linear and nonlinear optical responses.[6] Surface plasmon resonance (SPR), as one of the metal-nanoparticle properties, is caused by the coherent motion of the conduction-band electrons under an electromagnetic field [7,8] and often has a key role in the above-mentioned applications as it can amplify the local field. The electron-transport properties in metal-nanoparticle arrays [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] have also been explored and show Ohmic or Coulombic characteristics under various interparticle coupling strengths, [17] temperatures, [16][17][18][19] and local environments of the nanoparticles. [20] Recently, Jin et al. [26] have combined SPR with the electronic conductivity of a water-soluble Au colloid monolayer, which was formed by chemical absorption on an Al electrode coated with aluminum oxide. The results showed that SPR absorption of the Au-nanoparticle monolayer evidently caused the enhancement of current.However, the topology of the nanoparticle arrays, [13,21,22] such as voids and disorder, has an important influence on electron transport. Therefore, we believe that the topology of the nanoparticle monolayer would affect the process of their photoconductive behavior. Hydrophobic nanoparticles offer distinct advantages over hydrophilic ones in that the monolayer topology of the former can be well controlled by the solvent evaporation method or Langmuir-Blodgett (LB) technique. Herein, we report the synthesis of monodisperse 3 nm gold nanoparticles coated with n-C 12 H 25 SH (see transmission electron microscopy (TEM) images in the Supporting Information, Figure S1) by the modified method of Lin et al. [27] with distearyldimethylammonium bromide (DTAB). Using these hydrophobic particles, we fabricated monolayers with various degrees of coverage (q) by controlling the solvent evaporation time (t evp ), where q is defined as the percentage of the area occupied by nanoparticles in a unit area. The experimental results showed that the electron conduction of the hydrophobic gold-nanoparticle monolayers ( Figure S2) at low bias clearly increased [and hence the resistance decreased ( Figure S3)] with light irradiation. This change in photoresponse had a linear relationship with the degree of coverage of the gold-nanoparticle monolayers. Monochromic light experiments showed that the photoresponse effect arose from SPR absorption of gold nanoparticles in the monolayers.Gold-nanoparticle monolayers prepared during various t evp are investigated with TEM and UV/Vis spectroscopy. Figure 1 shows that the degree of coverage and the SPR peak clearly depend on solvent evaporation time: the longer the evaporation time, the higher the degree of coverage. At the same time, the SPR peak shifts from 544 to 560 nm with increasing degree of coverage. This finding is attributed to the increment in the die...

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Section: Introductionmentioning

confidence: 99%

The Photoelectric Response of Gold‐Nanoparticle Monolayers

Tang

Rong

et al. 2007

ChemPhysChem

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“…Earlier calculated ∆H, ∆G and pK Enol values for (MeO 2 C) 2 CHCONHPh at B3LYP/6-31G** are respectively -5.7 and -2.7 kcal/mol and 1.98. The following conclusions, based on the B3LYP/6-31+G* (B3LYP/6-31G**) values arise from Table 2: (a) For i-PrNHCOCH(SO 2 Ph)COMe ∆G for enolization on the acetyl group is 0.8 (-0.1) kcal/mol more negative than on the amide carbonyl.…”

Section: Dft Calculations Of K Enol Valuesmentioning

confidence: 93%

“…In contrast, the enols formed from proton transfer to the acetyl group were stable, and indeed the enol 7 was actually the product isolated. 2 R, R = Me, Ph (8f) (their calculated structures are given in Figure S1 in the Supporting Information) remain computationally stable but they were 19.5 (17.0) and 14.8 (15.5) kcal/mol, respectively, less stable than the isomeric enols 6.…”

Section: Structures In Solutionmentioning

confidence: 99%

“…The low enolization ability will be discussed in comparison with other EWGs, especially ester groups, in terms of these points. The electron-withdrawing ability of R'SO 2 , CO 2 R, NO 2 …”

Section: O H-o Valuesmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Examples of favorable Y,Y′ combinations include CO 2 R, CN, 2,6-9 CN, CN, 6,7 CO 2 R, competitive enolization between the COMe and CONHR carbonyls may give enol 7, and hence the product was assigned as 5o/6o/7o. Only 5e 16,17 and 5k 16 are known compounds.…”

Section: Introductionmentioning

confidence: 99%

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The low KEnol values of β-sulfonyl-substituted amides

Basheer¹,

Mishima²,

Rappoport³

2015

Arkivoc

Self Cite

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Amides substituted by one β-sulfonyl group and another β-sulfonyl, β-ester or β-CN group, form very low percentages of the corresponding enols, lower than for the β,β-diester and β-cyano, β-ester substituted systems, despite the equal or weaker electron delocalizing ability of the latter groups which help to stabilize the enols more than that of the sulfonyl group. This cannot be attributed to the non-planarity of the enols, since the calculated structures are planar. It is suggested that the sulfonyl-substituted amides are more stabilized than the β-ester-or β-cyanosubstituted amides. An amide substituted by β−nonafluorosulfonyl, β−acetyl groups enolizes on the acetyl group, forming a strong, nearly symmetrical intramolecular hydrogen bond. The use of 600 MHz NMR spectroscopy can extend the range of observable enols.

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Electrospray[+] tandem quadrupole mass spectrometry in the elucidation of ergot alkaloids chromatographed by HPLC: screening of grass or forage samples for novel toxic compounds

et al. 2005

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Ergot alkaloids are mycotoxins generated by grass and grain pathogens such as Claviceps, for example. Ergot alkaloid-poisoning syndromes, such as tall fescue toxicosis from endophyte-infected tall fescue grass, are important veterinary problems for cattle, horses, sheep, pigs and chickens, with consequent impact on food, meat and dairy industries. Damage to livestock is of the order of a billion dollars a year in the United States alone. HPLC with UV and fluorescence detection are the predominant means of ergot alkaloid determination, with focus on quantitation of the marker compound ergovaline, although ELISA methods are undergoing investigation. These techniques are excellent for rapid detection, but of poor specificity in defining new or poorly characterized ergot alkaloids and related compounds. This paper demonstrates the facility of using electrospray(+) mass spectrometry with multiple reaction monitoring (MRM) detection during chromatographic examination of ergot alkaloid standards of lysergic acid, lysergol, ergonovine, ergovaline, ergotamine, ergocornine, ergocryptine and ergocrystine by HPLC. Ergoline-8 position epimers could be separated on the gradient HPLC system for ergocornine, ergocrystine and ergonovine and appeared as shoulders for ergotamine and ergovaline; epimers generally showed different patterns of relative intensity for specific MRM transitions. There was reasonable correspondence between retention of standards on the 2-mm ESI(+)MS phenyl-hexyl-based reverse phase column and those on the 4-mm C18-based column. Since up to 10% of clinical cases involving toxin exposure display unidentified chromatographic peaks, 11 samples of feed components associated with such cases were studied with developed MRM methods to attempt elucidation of crucial components if possible. Ergotamine appeared in all, ergovaline appeared in five and ergocornine appeared in six; ergonovine, ergocryptine, ergocrystine and lysergol also appeared in several. In addition, molecular weights of compounds newly revealed by mass spectrometry suggested ergosine, ergostine and ergoptine in four samples, for which standards were not available. Dehydrated products of ergotamine, ergocrystine and ergocornine were discovered, along with dihydrogenated ergocrystine and ergocryptine in seven of the samples, and the issue was raised as to whether dehydration was strictly an instrument-derived artifact. Finally, five of the samples, along with fescue seed standard, evidenced one or more of 14 new ergot alkaloids ranging in size from 381 to 611 molecular weight and with key mass spectral characteristics of ergot alkaloids, specifically the pair of peaks m/z 223 and 208, corresponding to the ergoline ring system and its demethylated variant, respectively. It is anticipated that findings such as these will provide impetus to future development of analytical methodology for these heretofore relatively rare ergot alkaloid species.

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Cyano-, Nitro-, and Alkoxycarbonyl-Activated Observable Stable Enols of Carboxylic Acid Amides

Cited by 30 publications

References 30 publications

The Photoelectric Response of Gold‐Nanoparticle Monolayers

The Photoelectric Response of Gold‐Nanoparticle Monolayers

The low KEnol values of β-sulfonyl-substituted amides

Electrospray[+] tandem quadrupole mass spectrometry in the elucidation of ergot alkaloids chromatographed by HPLC: screening of grass or forage samples for novel toxic compounds

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