Mechanism of azo coupling reactions. Part 34. Reactivity of five-membered ring heteroaromatic diazonium ions

1986 ◽  
Vol 64 (6) ◽  
pp. 1102-1107 ◽  
Author(s):  
Heinz Diener ◽  
Heinrich Zollinger
Keyword(s):  
Rate Constants ◽  
Chemical Shifts ◽  
Reaction System ◽  
Membered Ring ◽  
Disulfonic Acid ◽  
Coupling Reactions ◽  
Azo Coupling ◽  
H Nmr ◽  
Ph Values ◽  
Diazonium Ions

The azo coupling reactions of six five-membered ring heteroaromatic diazonium ions with 2-naphthol-3,6-disulfonic acid are investigated kinetically at various pH values. The dependence of the measured rate constants on the acidity of the aqueous reaction system is evaluated. It can be shown that the 2-naphtholate-3,6-disulfonate trianion reacts 4 × 108–8 × 108 times faster than the 2-naphthol-3,6-disulfonate dianion. The rate constants of the six diazonium ions vary by more than four orders of magnitude. The logarithms of the rate constants of all comparable diazonium ions correlate linearly with 1H nmr chemical shifts of the respective unsubstituted heteroaromatic parent compounds. An analogous correlation was found for azo couplings with substituted benzenediazonium ions. Diazotization of heteroaromatic amines does not go to completion, rather to an equilibrium. It is shown therefore that in acidic coupling systems the azo compound is only the kinetically controlled product. The thermodynamic products are 1-nitroso-2-naphthol-3,6-disulfonic acid and the heteroaromatic amine.

Reactions of 4-Amino-3-penten-2-one and Its NSubstituted Derivatives with Diazonium Ions

1995 ◽  
Vol 60 (8) ◽  
pp. 1367-1379 ◽  
Author(s):  
Vladimír Macháček ◽  
Alexandr Čegan ◽  
Aleš Halama ◽  
Olga Rožňavská ◽  
Vojeslav Štěrba
Keyword(s):  
Coupling Reaction ◽  
Butyl Alcohol ◽  
Azo Compounds ◽  
Coupling Reactions ◽  
Azo Coupling ◽  
Alcohol Water ◽  
Diazonium Ions ◽  
Coupling Rate ◽  
Reaction Orders ◽  
Intramolecular Hydrogen

Azo coupling reactions of benzenediazonium salts with substituted 4-amino-3-penten-2-ones take place at the C-3 atom. 1H and 13C NMR spectroscopy has been used to study the structure of both the starting enaminones and coupling products. In CDCl3, 3-(4-chlorophenylhydrazono)-2-(4-methylphenylimino)-4-pentanone exists in hydrazo form whereas 4-amino-3-(4-chlorophenylazo)-3-penten-2-one is present as a mixture of two azo compounds differing probably in the arrangement of the intramolecular hydrogen bond. The azo coupling reaction kinetics have been studied in acetate buffers and methanol-water or tert-butyl alcohol-water mixtures. The coupling rate has been found independent of pH and buffer concentration. The reaction orders with respect to the starting compounds have been determined and the reaction mechanism is suggested. Linear dependence has been found between log kobs and substituent constants according to the Hammett or Yukawa-Tsuno equations.

The preparation and rearrangements of some 8,8-dimethylhomotropylium cations and their iron tricarbonyl complexes

1985 ◽  
Vol 63 (2) ◽  
pp. 418-425 ◽  
Author(s):  
Ronald F. Childs ◽  
Aravamuthan Varadarajan
Keyword(s):  
Low Temperatures ◽  
Chemical Shifts ◽  
Major Product ◽  
Membered Ring ◽  
Tricarbonyl Complex ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Free Energy Of Activation ◽  
Iron Tricarbonyl ◽  
Proton Chemical Shifts

The circumambulatory rearrangements of some 8,8-dimethylhomotropylium cations and their corresponding iron tricarbonyl complexes have been examined. 8,8-Dimethylhomotropylium cation, 4, has been prepared by protonation of 8,8-dimethyl-bicyclo[5.1.0]octa-3,5-dien-2-ol in FSO3H/SO2ClF. Evidence for homoaromatic delocalization in 4 was found in its characteristic 1H nmr spectrum, particularly when this was compared to that of the non-cyclically delocalized 8,8-dimethyl-bicyclo[5.1.0]octadienyliron tricarbonyl complex 7. Cation 4 was found to be stable at low temperatures but to isomerize to isopropyltropylium ion, 8, at −50 °C, [Formula: see text] The specifically deuterated cation 4D was prepared and a slow circumambulation of C8 around the basal 7-membered ring of this cation was found to occur at −90 °C. The free energy of activation for this circumambulation is 14.5 kcal/mol. Homotropylium cation 4 was also prepared by protonation of 8,8-dimethylbicyclo[3.2.1]octa-3,6-dien-2-ol, 14, at −120 °C. No evidence for the presence of the corresponding bicyclo[3.2.1]octadienyl ion 12 was obtained. The 2,8,8-trimethylhomotropylium cation, 17, was prepared and shown to undergo a circumambulatory rearrangement to give the 4,8,8-trimethyl substituted cation 20 as the major product. In this trimethyl series it also proved possible to generate the 2,8,8-trimethylbicyclo[3.2.1]octadienyl cation, 18, and observe its 1H nmr spectrum at very low temperatures (−116 °C). The proton chemical shifts of 18 suggest that the charge is predominantly located on the 3-carbon bridge. Cation 18 isomerized to 17, 20, and other products at temperatures above −100 °C. The 2,8,8-trimethylbicyclo[5.1.0]octadienyliron tricarbonyl complex 22 was also shown to undergo a circumambulatory rearrangement in which both C8 and the Fe(CO)3 grouping migrate.

1,4-Bis(p-pentazolylphenyl)butan, 1-p-Azidophenyl-4-p-pentazolylphenyl- butan und 1,4-Bis(p-azidophenyl)butan / 1,4-Bis(p-pentazolylphenyl)butane, 1-p-Azidophenyl-4-p-pentazolylphenyl-butane and 1,4-Bis(p-azidophenyl)butane

2004 ◽  
Vol 59 (6) ◽  
pp. 716-720 ◽  
Author(s):  
Frank Biesemeier ◽  
Klaus Harms ◽  
Ulrich Müller
Keyword(s):  
Low Temperature ◽  
Sodium Azide ◽  
Rate Constants ◽  
Nmr Spectra ◽  
Room Temperature ◽  
Fine Powder ◽  
Space Group ◽  
H Nmr ◽  
Diazonium Ions ◽  
C Nmr

1,4-Bis(p-pentazolylphenyl)butane (1), 1-p-azidophenyl-4-p-pentazolylphenyl-butane (2) and 1,4-bis(p-azidophenyl)butane (3) were obtained by the reaction of 1,4-diphenylbutane-4’,4”- bis(diazonium) ions with sodium azide in methanol at −50 °C. In the 1H and 13C NMR spectra the three compounds can be distinguished unequivocally. At −50 °C a mixture with a composition 1:2:3 of 10:30:60 was obtained. By recrystallization first from dichloromethane/methanol and then from dichloromethane/petroleum ether the pentazole components were enriched to a composition ratio of 21:62:17. The rate constants of the decompositions 1→2 and 2→3 at 0 °C were determined from the variation of the 1H NMR intensities. At room temperature all of the material is converted to 3. 3 crystallizes in two monoclinic modifications. At −70 °C a modification 3-LT having space group P21/c (a = 950.8, b = 1192.6, c = 701.3 pm, β = 92.55°, Z = 2; R = 0.075) was obtained. The modification crystallizing at room temperature (3-HT) has space group I2/a (a = 1514.5, b = 498.1, c = 2027.9 pm, β = 92.73°, Z = 4; R = 0.040). Whereas both modifications consist of nearly identical molecules, their packings are quite different. When the low temperature modification is warmed to room temperature, its crystals jump like flees and are disrupted to a fine powder.

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond; Adamantan-1-yl 3-Bromo-2,4,6-trimethylphenyl Ketone

1998 ◽  
Vol 63 (7) ◽  
pp. 955-966
Author(s):  
Eva Přibylová ◽  
Miroslav Holík
Keyword(s):  
Thermodynamic Parameters ◽  
Shape Analysis ◽  
Rate Constants ◽  
Line Shape ◽  
Microsoft Excel ◽  
Hindered Rotation ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Coalescence Temperature

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.

scholarly journals 13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

1999 ◽  
Vol 23 (1) ◽  
pp. 48-49
Author(s):  
Martín A. Iglesias Arteaga ◽  
Carlos S. Pérez Martinez ◽  
Roxana Pérez Gil ◽  
Francisco Coll Manchado
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
H Nmr ◽  
C 23 ◽  
Main Effects ◽  
Nmr Signals

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

scholarly journals Laccases: Versatile Biocatalysts for the Synthesis of Heterocyclic Cores

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3719
Author(s):  
Ana Catarina Sousa ◽  
Lígia O. Martins ◽  
M. Paula Robalo
Keyword(s):  
Membered Ring ◽  
Low Molecular Weight ◽  
Redox Potentials ◽  
Redox Mediators ◽  
Multicopper Oxidases ◽  
Phenothiazine Derivatives ◽  
Ph Values ◽  
Electron Shuttles ◽  
Specific Oxidation ◽  
Optimal Ph

Laccases are multicopper oxidases that have shown a great potential in various biotechnological and green chemistry processes mainly due to their high relative non-specific oxidation of phenols, arylamines and some inorganic metals, and their high redox potentials that can span from 500 to 800 mV vs. SHE. Other advantages of laccases include the use of readily available oxygen as a second substrate, the formation of water as a side-product and no requirement for cofactors. Importantly, addition of low-molecular-weight redox mediators that act as electron shuttles, promoting the oxidation of complex bulky substrates and/or of higher redox potential than the enzymes themselves, can further expand their substrate scope, in the so-called laccase-mediated systems (LMS). Laccase bioprocesses can be designed for efficiency at both acidic and basic conditions since it is known that fungal and bacterial laccases exhibit distinct optimal pH values for the similar phenolic and aromatic amines. This review covers studies on the synthesis of five- and six-membered ring heterocyclic cores, such as benzimidazoles, benzofurans, benzothiazoles, quinazoline and quinazolinone, phenazine, phenoxazine, phenoxazinone and phenothiazine derivatives. The enzymes used and the reaction protocols are briefly outlined, and the mechanistic pathways described.

scholarly journals Studies on the transannular Diels–Alder reaction of 15-membered macrocyclic trienes containing a trans-trans diene. Part I: Synthesis and isomerization of various model cyclopentadecatrienes

1995 ◽  
Vol 73 (10) ◽  
pp. 1675-1694 ◽  
Author(s):  
Dennis G. Hall ◽  
Renate Müller ◽  
Pierre Deslongchamps
Keyword(s):  
Aqueous Media ◽  
Alder Reaction ◽  
Membered Ring ◽  
Diels Alder ◽  
Coupling Reactions ◽  
Diels Alder Reaction ◽  
Trans Diene

The transannular Diels–Alder reaction of 15-membered macrocyclic trienes with a trans-trans-cis (TTC) olefin geometry can lead to A.B.C.[6.6.7] tricyclic products of trans-syn-trans (TST) and cis-syn-cis (CSC) stereochemistry whereas the TTT isomers can produce the trans-anti-cis (TAC) and cis-anti-trans (CAT) tricycles. In order to study the influence of the position (pro-6.6 or pro-6.7) and the nature (alkyl, alkoxymethyl, or formyl) of the dienophile substituent, a set of 10 model cyclopentadecatrienes was prepared. The synthesis of appropriately functionalized trisubstituted dienophile and diene synthons, as well as their coupling reactions affording acyclic precursors, is described in this paper (first in a series of two). A mild and efficient macrocyclization protocol yielded the required methyl- or alkoxymethyl-substituted cyclic substrates. Further transformations led to the formyl-substituted ones. In particular, the TTT macrocycles containing an enal as a dienophile could be completely isomerized to the corresponding TTC thermodynamic isomers in acidic aqueous media. Keywords: transannular, Diels–Alder, 15-membered ring, A.B.C.[6.6.7] tricycles, diterpene.

Chemical shifts of charge-transfer complexes and Buckingham equation

1990 ◽  
Vol 55 (9) ◽  
pp. 2131-2137
Author(s):  
Mahboob Mohammad ◽  
Ather Yaseen Khan ◽  
Tariq Mahmood ◽  
Ismat Fatima ◽  
Riffat Shaheen ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Nmr Spectra ◽  
Charge Transfer Complex ◽  
Chemical Shifts ◽  
Charge Transfer Complexes ◽  
Aprotic Solvents ◽  
Reaction Field ◽  
H Nmr ◽  
Spherical Cavities ◽  
Dipolar Aprotic Solvents

The 1H NMR spectra of the charge-transfer complex of 1-ethyl-4-methoxycarbonylpyridinium iodide have been recorded in various dipolar aprotic solvents. An attempt is made to interpret the chemical shifts in terms of Buckingham's reaction field equation for spherical cavities. A linear dependence has been found between the δ(2,6) values and the square of dielectric function for a spherical cavity, which confirms the validity of the Buckingham equation for this class of compounds.

Sign in / Sign up

Export Citation Format

Share Document