Infrared Studies of the Isomerization of Cis-Pd(NH3)2X2

Palladium complexes of the type cis-PdL2X2 have been found to be unstable at room temperature and isomerize to the corresponding trans isomers. Neglecting lattice interactions, symmetry considerations would predict two Pd–N stretching vibrations. These vibrations have been observed at 495 and 476 cm−1 for the cis-chloride isomer and at 480 and 460 cm−1 for the cis-bromide isomer. The trans isomer, by the same considerations, should have but one Pd–N stretching vibration. This vibration was observed for the trans-chloride isomer at 496 cm−1 and for the trans-bromide isomer at 490 cm−1. It has been found that as isomerization proceeds, from the cis to the trans forms, the lower Pd–N stretching vibration decreases in intensity and eventually disappears. The intensity changes for these vibrations over a period of 72 h indicated that the reaction follows a first-order rate law. A reaction mechanism has been proposed.

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Infrared spectra and substituent effects in 2-(3-, and 4-substituted phenylmethylene)-1,3-cycloheptanediones

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19830586 ◽

1983 ◽

Vol 48 (2) ◽

pp. 586-595 ◽

Cited By ~ 3

Author(s):

Alexander Perjéssy ◽

Pavol Hrnčiar ◽

Ján Šraga

Keyword(s):

Substituent Effects ◽

Phenyl Group ◽

Wave Number ◽

Vibrational Coupling ◽

Wave Numbers ◽

Stretching Vibration ◽

Stretching Vibrations ◽

The Relationship ◽

Derivatives Of ◽

Effect Of Structure

The wave numbers of the fundamental C=O and C=C stretching vibrations, as well as that of the first overtone of C=O stretching vibration of 2-(3-, and 4-substituted phenylmethylene)-1,3-cycloheptanediones and 1,3-cycloheptanedione were measured in tetrachloromethane and chloroform. The spectral data were correlated with σ+ constants of substituents attached to phenyl group and with wave number shifts of the C=O stretching vibration of substituted acetophenones. The slope of the linear dependence ν vs ν+ of the C=C stretching vibration of the ethylenic group was found to be more than two times higher than that of the analogous correlation of the C=O stretching vibration. Positive values of anharmonicity for asymmetric C=O stretching vibration can be considered as an evidence of the vibrational coupling in a cyclic 1,3-dicarbonyl system similarly, as with derivatives of 1,3-indanedione. The relationship between the wave numbers of the symmetric and asymmetric C=O stretching vibrations indicates that the effect of structure upon both vibrations is symmetric. The vibrational coupling in 1,3-cycloheptanediones and the application of Seth-Paul-Van-Duyse equation is discussed in relation to analogous results obtained for other cyclic 1,3-dicarbonyl compounds.

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The kinetics of hydration of tricalcium silicate

Canadian Journal of Chemistry ◽

10.1139/v70-554 ◽

1970 ◽

Vol 48 (21) ◽

pp. 3291-3299 ◽

Cited By ~ 4

Author(s):

K. G. McCurdy ◽

B. P. Erno

Keyword(s):

Reaction Mechanism ◽

Intermediate Product ◽

Activation Energies ◽

Tricalcium Silicate ◽

Rate Data ◽

Large Excess ◽

First Order ◽

Kinetics Of ◽

Subsequent Decomposition

An investigation has been made of the kinetics of hydration of tricalcium silicate at several temperatures in a large excess of water in the presence of various added ions. The rate data have been interpreted by a reaction mechanism which involves: (a) the first order hydration of tricalcium silicate to form an intermediate product, 1.5CaO•SiO2, which can react by two pathways, (b) the direct first order decomposition of intermediate, 1.5CaO•SiO2, to form lime and silica or (b′) complexing of intermediate with silica and subsequent decomposition to form lime and silica. This reaction mechanism predicts the rate of production of base during the hydration. The effect of various added ions is interpreted in terms of the proposed mechanism.Rate constants and activation energies for the various steps in the proposed mechanism are reported.

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Infrared studies on rotational isomerism. III. 2-Chloro- and 2-bromo-ethanol

Canadian Journal of Chemistry ◽

10.1139/v69-148 ◽

1969 ◽

Vol 47 (6) ◽

pp. 901-910 ◽

Cited By ~ 50

Author(s):

Paul Buckley ◽

Paul A. Giguère ◽

Michel Schneider

Keyword(s):

Hydrogen Bonding ◽

Intramolecular Hydrogen Bonding ◽

Rotational Isomerism ◽

Apparent Discrepancy ◽

Trans Isomers ◽

Kcal Mole ◽

Infrared Studies ◽

Isotopic Molecule ◽

Intramolecular Hydrogen ◽

Unambiguous Assignment

The relative intensities of the C—X stretching bands of the gauche and trans isomers in the vapor were measured as a function of temperature up to 165 °C for 2-chloroethanol, and up to 130 °C for 2-bromoethanol. From these the enthalpy differences between the two isomers were found to be 1.20 and 1.45 ± 0.1 kcal mole−1 respectively for the two halogenated ethanols. Similar measurements on the O—H stretching bands gave values higher than the above by 0.45 kcal mole−1 for both compounds. This apparent discrepancy is interpreted as due to a second gauche isomer, the OH group of which is not engaged in intramolecular hydrogen bonding, and which is less stable than the trans isomer.A study of the isotopic molecule ClCH2—CH2OD has led to unambiguous assignment of the OH bending and torsional frequencies. The spectra of the solid show that 2-chloroethanol can exist in two different crystalline phases: a stable one consisting of gauche molecules only, and a metastable one containing both isomers.

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The reaction of μ-oxo-bis(phthalocyaninato)iron(III) with hydrogen sulphide in the presence of pyridine: Evidence for axial coordination of dichloromethane

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424605000265 ◽

2005 ◽

Vol 09 (03) ◽

pp. 198-205 ◽

Cited By ~ 1

Author(s):

Fabrizio Monacelli ◽

Elisa Viola

Keyword(s):

Reaction Mechanism ◽

Linear Function ◽

Rate Constant ◽

Hydrogen Sulphide ◽

Stoichiometric Ratio ◽

First Order ◽

Axial Coordination ◽

Elementary Sulphur ◽

Increasing Function ◽

Limiting Value

The oxo-bridged complex ( py ) FePc - O - FePc ( py ) ( py = pyridine , Pc = phthalocyaninato dianion) reacts in dichloromethane with hydrogen sulphide giving elementary sulphur and the reduced ( py )2( FePc ) complex in the stoichiometric ratio 1:1. Under excess py and H2S , the reaction is first-order and the rate constant at a given py concentration is an increasing function of the reducing agent concentration, with asymptotic tendency to a limiting value. This latter depends on the pyridine concentration being higher the lower is the base concentration. When the reaction is carried out in pure pyridine, the rate constant is, instead, a strictly linear function of [ H2S ], with zero intercept. A reaction mechanism is proposed where the dichloromethane is directly involved in the axial coordination about the iron centers and H2S competes efficiently with both pyridine and solvent.

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Synthesis of spiro[dihydropyridine-oxindoles] via three-component reaction of arylamine, isatin and cyclopentane-1,3-dione

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.9.2 ◽

2013 ◽

Vol 9 ◽

pp. 8-14 ◽

Cited By ~ 28

Author(s):

Yan Sun ◽

Jing Sun ◽

Chao-Guo Yan

Keyword(s):

Acetic Acid ◽

Reaction Mechanism ◽

Room Temperature ◽

The Other ◽

Other Hand ◽

Three Component Reaction ◽

High Yields

A fast and convenient protocol for the synthesis of novel spiro[dihydropyridine-oxindole] derivatives in satisfactory yields was developed by the three-component reactions of arylamine, isatin and cyclopentane-1,3-dione in acetic acid at room temperature. On the other hand the condensation of isatin with two equivalents of cyclopentane-1,3-dione gave 3,3-bis(2-hydroxy-5-oxo-cyclopent-1-enyl)oxindole in high yields. The reaction mechanism and substrate scope of this novel reaction is briefly discussed.

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Engineering Increased Stability in the Antimicrobial Peptide Pediocin PA-1

Applied and Environmental Microbiology ◽

10.1128/aem.66.11.4798-4802.2000 ◽

2000 ◽

Vol 66 (11) ◽

pp. 4798-4802 ◽

Cited By ~ 46

Author(s):

Line Johnsen ◽

Gunnar Fimland ◽

Vincent Eijsink ◽

Jon Nissen-Meyer

Keyword(s):

Antimicrobial Peptide ◽

Molecular Mass ◽

Room Temperature ◽

Bacteriocin Activity ◽

Food Preservative ◽

Food Grade ◽

First Order ◽

Methionine Residue ◽

First Order Kinetics

ABSTRACT Pediocin PA-1 is a food grade antimicrobial peptide that has been used as a food preservative. Upon storage at 4°C or room temperature, pediocin PA-1 looses activity, and there is a concomitant 16-Da increase in the molecular mass. It is shown that the loss of activity follows first-order kinetics and that the instability can be prevented by replacing the single methionine residue (Met31) in pediocin PA-1. Replacing Met by Ala, Ile, or Leu protected the peptide from oxidation and had only minor effects on bacteriocin activity (for most indicator strains 100% activity was maintained). Replacement of Met by Asp was highly deleterious for bacteriocin activity.

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The resonance Raman spectra and excitation profiles of some 4-sulfamylazobenzenes

Canadian Journal of Chemistry ◽

10.1139/v77-203 ◽

1977 ◽

Vol 55 (9) ◽

pp. 1444-1453 ◽

Cited By ~ 28

Author(s):

Kamal Kumar ◽

P. R. Carey

Keyword(s):

Raman Spectrum ◽

Raman Spectra ◽

Resonance Raman ◽

Valence Bond ◽

Wavelength Dependence ◽

Accurate Estimation ◽

Intensity Changes ◽

Stretching Vibration ◽

Resonance Raman Spectra ◽

Frequency Changes

The resonance Raman spectra of three pharmacologically important sulfonamides, 4-sulfamyl-4′-dimethylaminoazobenzene (1), 4-sulfamyl-4′-hydroxyazobenzene (2), and 4-sulfamyl-4′-aminoazobenzene (3), are compared with those of analogues lacking the sulfonamide group. The —SO2NH2 moiety does not directly contribute intense or moderately intense bands to the resonance Raman spectra of 1, 2, and 3. However, —SO2NH2 ionization is reflected by frequency changes in a band near 1140 cm−1 and intensity changes in the 1420 cm−1 region. The normal Raman spectrum of 2 confirms that the intensity changes reflect —SO2NH2 ionization rather than unrelated changes in vibronic coupling. The effect of —OH ionization on the resonance Raman spectrum of 2 emphasizes that caution must be exercised when relating spectral perturbations to changes in contributions from valence bond type structures. Resonance Raman excitation profiles for the 1138, 1387, and 1416 cm−1 bands of 2 show that these bands gain intensity by coupling with the electronic transitions in the 240 to 450 nm region and that, more than 1000 cm−1 to the red of λmax, the wavelength dependence can be closely reproduced by the FB type terms of Albrecht and Hutley. The excitation profile for each band shows evidence for structure in the 470 nm region, although lack of sufficient excitation wavelengths prevents accurate estimation of the spacing. Under conditions of rigorous resonance the intense Raman lines all occur in the 1400 cm−1 region, i.e. they are 'bunched' in the region known to contain the —N=N— stretching vibration.

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TfOH-Promoted Reaction of 2,4-Diaryl-1,1,1-Trifluorobut-3-yn-2-oles with Arenes: Synthesis of 1,3-Diaryl-1-CF3-Indenes and Versatility of the Reaction Mechanisms

Molecules ◽

10.3390/molecules23123079 ◽

2018 ◽

Vol 23 (12) ◽

pp. 3079 ◽

Cited By ~ 4

Author(s):

Aleksey V. Zerov ◽

Anna N. Kazakova ◽

Irina A. Boyarskaya ◽

Taras L. Panikorovskii ◽

Vitalii V. Suslonov ◽

...

Keyword(s):

Reaction Mechanism ◽

Reaction Mechanisms ◽

Room Temperature ◽

Ring Closure ◽

Nucleophilic Attack ◽

New Process ◽

Intramolecular Ring ◽

Propargyl Alcohols

The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF3-substituted diaryl propargyl alcohols) with arenes in CH2Cl2 afford 1,3-diaryl-1-CF3-indenes in yields up to 84%. This new process for synthesis of such CF3-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples. The proposed reaction mechanism invokes the formation of highly reactive CF3-propargyl cation intermediates that can be trapped at the two mesomeric positions by the intermolecular nucleophilic attack of an arene partner with a subsequent intramolecular ring closure.

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