Enols of Carboxylic Acid Amides with β-Electron-Withdrawing Substituents

Mukhopadhyaya, Jayanta K.; Sklenák, and Stepan; Rappoport, Zvi

doi:10.1021/ja992059f

Cited by 59 publications

(93 citation statements)

References 59 publications

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“…[4] Very large dihedral angles, 51-89 • , have also been determined in (N,N-disubstituted) 1,1-diamino-2,2-dinitroethylenes. [5] Rotational barriers [6] and X-ray crystal structures [3,[7][8][9][10][11] of several other push-pull ethylenes are described in the literature. The twisting has been discussed in terms of contributions from the π-electron energy (favouring planarity) and the steric strain energy (opposing planarity).…”

Section: Introductionmentioning

confidence: 99%

Twisted Push - Pull Ethylenes

et al. 2008

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As determined by X-ray crystallography, Meldrum's acid derivatives 5, 6, and 8 feature dihedral angles around the central C5=C7 double bond of 14-35 • , whereas for the anion 9 this angle is 90 • . Density functional theory and MP2 calculations are in agreement with the experimental X-ray data for compounds 5-8, but for anion 9 an angle of only ∼65 • is predicted. It is concluded that a part of the torsion is due to packing forces in the crystal. It is further concluded that these molecules undergo rapid rotation about the central CC bonds at room temperature (calculated activation barriers 5-14 kcal mol −1 ).

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Section: Introductionmentioning

confidence: 99%

Twisted Push - Pull Ethylenes

et al. 2008

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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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“…However, enols can be dramatically stabilized by the introduction of bulky groups onto the carbon α to the carbonyl group 5,6 and in some cases the enol may then be the thermodynamically stable tautomer, 7 although not kinetically. 8 The pentamethylphenyl group is an effective bulky substituent and provides the necessary stability for enediols (enol form of carboxylic acids and esters). 9 The chemistry of these enols, (derived from carbonyl containing compounds other than ketones, including carboxylic acids and esters) has been of some interest.…”

Section: Introductionmentioning

confidence: 99%

Tautomerism of lactones and related compounds. Mass spectrometric data and theoretical calculations

Allegretti¹,

Cortizo²,

Guzmán³

et al. 2003

Arkivoc

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The enolization degree of lactones and esters is favoured by the oxygen-sulfur exchange in the respective functional groups. The analysis of the corresponding mass spectra has allowed unambiguous assignment of some fragments to specific tautomers and establishment of an acceptable correlation between ion abundances ratios and AM1 theoretical calculations. This supports mass spectrometry as an adequate tool to evaluate the tautomerism of neutral species.

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Enols of Carboxylic Acid Amides with β-Electron-Withdrawing Substituents

Cited by 59 publications

References 59 publications

Twisted Push - Pull Ethylenes

Twisted Push - Pull Ethylenes

The Photoelectric Response of Gold‐Nanoparticle Monolayers

Tautomerism of lactones and related compounds. Mass spectrometric data and theoretical calculations

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