Carbon versus oxygen nucleophilic selectivity in the reaction of the aryloxide ions, 2,6- and 3,5-di-tert-butylphenoxide, with the 2-[(nitro)\dn6 xaryl]-4,6-dinitrobenzotriazole 1-oxide series of super-electrophiles. Stereoelectronic factors on C-7 Meisenheimer complex formation versus C-1' SNAr displacement

1998 ◽  
Vol 76 (6) ◽  
pp. 662-671 ◽  
Author(s):  
Julian M Dust ◽  
Richard A Manderville
Keyword(s):  
Nmr Spectroscopy ◽  
Nucleophilic Aromatic Substitution ◽  
Nucleophilic Attack ◽  
Aromatic Substitution ◽  
Factors Affecting ◽  
H Nmr ◽  
Sterically Demanding ◽  
Biphenyl Derivative ◽  
First Time ◽  
Electrophilic Site

The 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides (1, Pi-DNBT (x = 3); 2, DNP-DNBT (x = 2); 3, NP-DNBT (x = 1)) are electron-deficient nitro-substituted heteroaromatic substrates that possess two sites for nucleophilic attachment: C-7 and C-1'. Generally, attack at the super-electrophilic C-7 site yields spectroscopically observable anionic sigma -bonded adducts, whereas attack at C-1' leads to displacement products in an overall process of nucleophilic aromatic substitution (SNAr). To gain an understanding of the factors affecting C-1' versus C-7 attack by potentially ambident aryloxide (C- and O-)nucleophiles, we have monitored the reactions of 1-3 with 2,6-di-tert-butylphenoxide (2,6-ArO-) and 3,5-di-tert-butylphenoxide (3,5-ArO-) using 400 MHz 1H NMR spectroscopy (deuterated dimethyl sulfoxide solvent at ambient temperature). The results indicate that 2,6-ArO- acts only as a C-nucleophile with O-attack precluded, presumably by the sterically demanding tert-butyl groups flanking the O-nucleophilic centre. Although 2,6-ArO- reacts preferentially at C-7 of 1-3, the biphenyl derivative that arises from C-1' attack is also observed with 1, the first time that C-nucleophilic attack has been seen at this electrophilic site. In contrast, 3,5-ArO- acts only as an O-nucleophile, also as a consequence of the steric hindrance to the C-4 position; this aryloxide reacts entirely at C-1' of Pi-DNBT but also exclusively at C-7 of 3. However, with DNP-DNBT, 2, both the C-7 O-adduct and C-1' displacement products are noted; attack at C-1' is dominant. The selectivity (C-7 versus C-1') found in these reactions is discussed with emphasis given to stereoelectronic factors that may stabilize the putative C-1' O-adducts.Key words: aryloxides, super-electrophiles, Meisenheimer complexes, 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides.

scholarly journals Synthesis of Novel Fluorescent Sensors Based on Naphthalimide Fluorophores for the Highly Selective Hg2+-Sensing

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Yordkhuan Tachapermpon ◽  
Pornthip Piyanuch ◽  
Narupon Prapawattanapol ◽  
Kanjarat Sukrat ◽  
Kullatat Suwatpipat ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Fluorescent Sensors ◽  
Nucleophilic Aromatic Substitution ◽  
Aromatic Substitution ◽  
One Pot ◽  
H Nmr ◽  
Sensitivity And Selectivity ◽  
New Sensors ◽  
Interfering Ions ◽  
C Nmr

With an aim to develop the new sensors for optical detection of Hg2+ions, two novel fluorometric sensors were designed and successfully prepared using 2-(3-(2-aminoethylsulfanyl)propylsulfanyl)ethanamine and one or twoN-methylnaphthalimide moieties (1and2). Sensor1was obtained viaN-alkylation,N-imidation and a one-pot nucleophilic aromatic substitution, andN-formylation of the amine, while sensor2was prepared viaN-alkylation,N-imidation, and nucleophilic aromatic substitution. The characterization, including1H NMR,13C NMR, and mass spectrometry, was then performed for1and2. The Hg2+-binding behaviors of the sensors were investigated in terms of sensitivity and selectivity by fluorescence spectroscopy. Sensor1especially provided the reversible and highly Hg2+-selective ON-OFF fluorescence behavior by discriminating various interfering ions such as Pb2+, Co2+, Cd2+, Mn2+, Fe2+, K+, Na+, and in particular Cu2+and Ag+with a detection limit of 22 ppb toward Hg2+ions.

Mechanisms and models for homogeneous copper mediated ligand exchange reactions of the type: CuNu + ArX → ArNu + CuX

1985 ◽  
Vol 63 (1) ◽  
pp. 111-120 ◽  
Author(s):  
Christiane Couture ◽  
Anthony James Paine
Keyword(s):  
Molecular Design ◽  
Nucleophilic Aromatic Substitution ◽  
Common Mechanism ◽  
Aromatic Substitution ◽  
Exchange Reactions ◽  
Design And Synthesis ◽  
Alkyl Groups ◽  
Leaving Group ◽  
First Time ◽  
Redox Equilibria

The title reactions are an important class of copper mediated nucleophilic aromatic substitution processes, which constitute a useful tool in the molecular design and synthesis of small molecules. We report the results of extensive investigation of these processes, primarily focussing on cyanodeiodination (ArI + CuCN → CuI + ArCN). Among the interesting features of these processes are: (a) an unusual rate equation involving autocatalysis by CuI product; (b) retardation by both excess nucleophile (as KCN) and excess leaving group (as KI), which compete with ArX to complex with CuNu; (c) only cuprous nucleophiles are active (ligand exchanged products from cupric salts arise from prior redox equilibria which form CuNu); (d) the halogen effect is large (kI ~ 40–100 kBr ~ 300–5000kCl) but the Hammett ρ value is zero; (e) ortho-alkyl groups do not hinder the reaction (and actually cause mild acceleration by relief of steric strain). Finally, the introduction of an ortho-COO− group accelerates the reaction by a factor of 104–105, but the general features of the accelerated reactions are also the same, again indicating a common mechanism, with entropic acceleration by ortho-carboxylate. Both kinetic and thermodynamic factors were considered in detail, the latter apparently for the first time. Applications to practical syntheses are considered, and novel mechanistic models for these interesting processes are discussed.

scholarly journals Quantum Chemical Characterization of Factors Affecting the Neutral and Radical-Cation Newman-Kwart Reactions

2018 ◽  
Author(s):  
Sina Chiniforoush ◽  
Christopher J. Cramer
Keyword(s):  
Aromatic Ring ◽  
Radical Cation ◽  
Quantum Chemical ◽  
Chemical Characterization ◽  
Nucleophilic Aromatic Substitution ◽  
Stationary Points ◽  
Aromatic Substitution ◽  
Free Energies ◽  
Factors Affecting ◽  
Thermal Reactions

Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol–1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol–1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality.

Isolierungen und 11C-NMR-Spektroskopie von Indoleninalkaloiden / Isolation and 13C NMR Spectroscopy of Indolenine Alkaloids

1982 ◽  
Vol 37 (4) ◽  
pp. 494-498 ◽  
Author(s):  
Mohammad Ataullah Khan ◽  
Hans Horn ◽  
Wolfgang Voelter
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Nmr Spectra ◽  
13C Nmr Spectroscopy ◽  
H Nmr ◽  
First Time

The indolenine alkaloids raucaffricine and perakine were isolated from Rauwolfia caffra Sonder and their PFT 13C{1H}-NMR spectra studied for the first time. The interpretations of their spectra were accomplished in correlating with those of quinuclidine, indole, methyl-α-D-galactopyranoside, methyl-β-D-galactopyranoside, methyl-2,6-di-O-methyl-α-D-galactopyranoside and methyl-3-O-methyl-β-D-galactopyranoside.

Uncatalyzed CO2Li-Mediated SNAr Reaction of Unprotected Benzoic Acids via Silicon Trickery

2016 ◽  
Vol 69 (3) ◽  
pp. 307 ◽  
Author(s):  
Mickael Belaud-Rotureau ◽  
Anne-Sophie Castanet ◽  
Thi Huu Nguyen ◽  
Jacques Mortier
Keyword(s):  
Methoxy Group ◽  
Intermediate Formation ◽  
Coupling Reaction ◽  
Nucleophilic Aromatic Substitution ◽  
Direct Access ◽  
Nucleophilic Attack ◽  
Benzoic Acids ◽  
Aromatic Substitution ◽  
Snar Reaction ◽  
Ketone Formation

The alkyl and aryllithium nucleophilic aromatic substitution (SNAr) displacement of a fluoro or methoxy group from unprotected 2-fluoro/methoxybenzoic acids is discussed. It was discovered that a TMS group located at the C6-position ortho to the carboxyl group shields effectively the carboxylate against nucleophilic attack, thus reducing dramatically ketone formation, and reorients nucleophilic substitution to the C2-position. The reactions with fluoro-substituted substrate 7 proceed efficiently; in contrast, the use of methoxy-functionalized benzoic acid 8 only affords moderate yields with s-BuLi and PhLi. This uncatalyzed coupling reaction, which provides a direct access to biaryl compounds, presumably proceeds by an addition–elimination sequence via intermediate formation of a resonance-stabilized pentavalent silalactone-Meisenheimer complex.

scholarly journals NMR Spectroscopy of Human Eye Tissues: A New Insight into Ocular Biochemistry

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Tomasz Kryczka ◽  
Edward Wylęgała ◽  
Dariusz Dobrowolski ◽  
Anna Midelfart
Keyword(s):  
Nmr Spectroscopy ◽  
Human Eye ◽  
H Nmr ◽  
Biochemical Compounds ◽  
Eye Tissues ◽  
Metabolic Properties ◽  
Human Eyes ◽  
First Time ◽  
Insight Into ◽  
Complex Organ

Background. The human eye is a complex organ whose anatomy and functions has been described very well to date. Unfortunately, the knowledge of the biochemistry and metabolic properties of eye tissues varies. Our objective was to reveal the biochemical differences between main tissue components of human eyes.Methods. Corneas, irises, ciliary bodies, lenses, and retinas were obtained from cadaver globes 0-1/2 hours postmortem of 6 male donors (age: 44–61 years). The metabolic profile of tissues was investigated with HR MAS1H NMR spectroscopy.Results. A total of 29 metabolites were assigned in the NMR spectra of the eye tissues. Significant differences between tissues were revealed in contents of the most distant eye-tissues, while irises and ciliary bodies showed minimal biochemical differences. ATP, acetate, choline, glutamate, lactate, myoinositol, and taurine were identified as the primary biochemical compounds responsible for differentiation of the eye tissues.Conclusions. In this study we showed for the first time the results of the analysis of the main human eye tissues with NMR spectroscopy. The biochemical contents of the selected tissues seemed to correspond to their primary anatomical and functional attributes, the way of the delivery of the nutrients, and the location of the tissues in the eye.

Spectroscopic Characterization of the Selenium-Rich Heterocycles Se5S, Se7S, and 1,5-Se6S2

1991 ◽  
Vol 46 (12) ◽  
pp. 1674-1678 ◽  
Author(s):  
Ralf Steudel ◽  
Maria Papavassiliou ◽  
Frank Baumgart
Keyword(s):  
Nmr Spectroscopy ◽  
Nmr Spectra ◽  
Spectroscopic Characterization ◽  
Reversed Phase ◽  
Nucleophilic Attack ◽  
Crystal Data ◽  
Reversed Phase Hplc ◽  
Cyclic Molecules ◽  
First Time

Se5S in CS2 solution at 20°C spontaneously decomposes to give a mixture of 8 selenium-rich cyclic molecules which have been identified by reversed-phase HPLC and 77Se NMR spectroscopy as Se6, Se7, Se8, Se6S, Se7S, 1,2-Se6S2, 1,5-Se6S2, and 1,4-Se4S2. NMR spectra of Se5S, Se7S, and 1,5-Se6S2 have been measured for the first time; Raman spectra of solid Se5S and Se7S as well as crystal data of Se7S are reported in addition. A mechanism based on nucleophilic attack on Se5S is proposed for the formation of the products.

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