Condensation of schiff bases with compounds containing labile hydrogen atoms

1971 ◽  
Vol 7 (4) ◽  
pp. 484-487 ◽  
Author(s):  
N. S. Kozlov ◽  
G. V. Vorob'eva
Keyword(s):  
Schiff Bases ◽  
Labile Hydrogen ◽  
Hydrogen Atoms

The non-isothermal oxidation of 2 -methylpentane. - III. The reaction at high pressure

1969 ◽  
Vol 313 (1513) ◽  
pp. 261-297 ◽  
Keyword(s):  
High Temperatures ◽  
Isothermal Oxidation ◽  
Gas Liquid Chromatography ◽  
Labile Hydrogen ◽  
Chain Process ◽  
Unimolecular Decomposition ◽  
Hydrogen Atoms ◽  
Radical Chain ◽  
Cool Flame ◽  
Alkylperoxy Radicals

The non-isothermal oxidation of 2-methylpentane has been studied at pressures of 1-4 MN m -2 and temperatures of 440 to 660 °C in an arrested-piston rapid-compression machine. The variations with pressure and temperature of the induction periods leading to cool-flame reaction and hot ignition have been determined, and the products of the reaction have been analysed by gas-liquid chromatography. At high temperatures and pressures the cool-flame reaction occurs by a free-radical chain process in which homogeneous isomerization and subsequent decomposition of alkylperoxy radicals propagate the chain. The resulting propa­gation cycle is substantially the same as that which has been established at lower tempera­tures and subatmospheric pressures. At high temperatures and pressures the reaction is, however, even more unselective, and oxidation of β -hydroperoxyalkyl radicals competes more successfully with their unimolecular decomposition, thus leading to the formation of β -ketoaldehydes. These compounds, together with the conjugated unsaturated carbonyl compounds, account quantitatively for the absorption of ultraviolet light by reacting 2-methylpentane/air mixtures. The mechanism of chain branching in the cool-flame reaction probably involves the pyrolysis of hydroperoxides. In the second stage of two-stage ignition, the propagation cycle is the same as that occurring in the cool flame but the important difference is that the cool flame has formed substantial concentrations of compounds with labile hydrogen atoms; these react readily with alkylperoxy radicals to form hydroperoxides, the pyrolysis of which again branches the chain.

scholarly journals XLVIII.—The absorption spectra of substances containing labile hydrogen atoms

1913 ◽  
Vol 103 (0) ◽  
pp. 406-419
Author(s):  
Peter Joseph Brannigan ◽  
Alexander Killen Macbeth ◽  
Alfred Walter Stewart
Keyword(s):  
Absorption Spectra ◽  
Labile Hydrogen ◽  
Hydrogen Atoms

scholarly journals Water hydrogen uptake in biomolecules detected via nuclear magnetic phosphorescence

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Aude Sadet ◽  
Cristina Stavarache ◽  
Florin Teleanu ◽  
Paul R. Vasos
Keyword(s):  
Spectroscopic Method ◽  
Hydrogen Uptake ◽  
Resonance Spectroscopy ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
Surrounding Water ◽  
Structural Investigations ◽  
Molecular Framework ◽  
Water Hydrogen ◽  
Nuclear Magnetic

AbstractWe introduce a new symmetry-based method for structural investigations of areas surrounding water-exchanging hydrogens in biomolecules by liquid-state nuclear magnetic resonance spectroscopy. Native structures of peptides and proteins can be solved by NMR with fair resolution, with the notable exception of labile hydrogen sites. The reason why biomolecular structures often remain elusive around exchangeable protons is that the dynamics of their exchange with the solvent hampers the observation of their signals. The new spectroscopic method we report allows to locate water-originating hydrogens in peptides and proteins via their effect on nuclear magnetic transitions similar to electronic phosphorescence, long-lived coherences. The sign of long-lived coherences excited in coupled protons can be switched by the experimenter. The different effect of water-exchanging hydrogens on long-lived coherences with opposed signs allows to pinpoint the position of these labile hydrogen atoms in the molecular framework of peptides and proteins.

scholarly journals Synthesis and Properties of Peroxy Oligomers Obtained by Telomerization Effects of the Presence of Bases

2016 ◽  
Vol 5 (4) ◽  
pp. 261
Author(s):  
Michael M. Bratychak ◽  
Volodymyr B. Vostres ◽  
Marc J.M. Abadie
Keyword(s):  
Unsaturated Polyester ◽  
Diglycidyl Ether ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
Molecular Weights ◽  
Chemical Structures ◽  
Direct Titration ◽  
Mobile Hydrogen ◽  
One Step ◽  
Labile Hydrogen Atom

<p>New bifunctional oligomers bearing peroxy groups have been synthesized by telomerization in one step reaction. For obtaining oligoperoxides (PO) by telomerization method, epoxide compounds will react with substances containing labile hydrogen atom. Using the principle of stochiometric imbalance between diepoxy compounds and substances with mobile hydrogen atoms and employing a functional peroxide as telogen, the synthesis of PO was studied. 2,2–Di[4–(2,3–epoxy–1-propoxy)phenyl]–propane (diglycidyl ether of diphenylol propane - DGEDPP), 1,2–Di (2,3–epoxy–1-propoxy) ethane (diglycidyl ether of ethylene glycol - DGEEG) and 1,2–Epoxy–3–tert–butylperoxypropane (EP) have been synthesized by methods reported in the literature. Chemical structures have been confirmed by NMR and FTIR, number-average molecular weights M<sub>n</sub> of PO<sub>s</sub> by cryoscopy, active oxygen content [O]<sub>act</sub>. for PO<sub>s</sub> was determined by iodometry and epoxy number (<em>e.n</em>.) for PO<sub>s</sub> was measured via direct titration of PO samples. A 50% solution of potassium or sodium isopropylates in 2-propanol is used to catalyze the telomerisation. Different parameters such as ratio of components, temperature, reaction time have been optimized in vu to get well defined peroxy oligomers. The presence of peroxy groups in synthesized POs allows us to employ these compounds as curing agents for polymers containing unsaturated double bonds and may be used to improve performance of unsaturated polyester GFR systems.</p>

Methods to Access 2-aminobenzimidazoles of Medicinal Importance

2020 ◽  
Vol 23 (23) ◽  
pp. 2573-2597
Author(s):  
Alejandro Cruz ◽  
Itzia I. Padilla Martínez ◽  
Angel A. Ramos-Organillo
Keyword(s):  
Medicinal Chemistry ◽  
Biological Activities ◽  
Building Blocks ◽  
Electron System ◽  
Clinical Applications ◽  
Amino Group ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
Lone Pairs ◽  
Guanidine Moiety

: Benzimidazole (BI) and derivatives are interesting because several of these compounds have been found to have a diversity of biological activities with clinical applications. In view of their importance, the synthesis of BI and its derivatives is still considered as a challenge for synthetic chemists. Examples of compounds used in medicinal chemistry containing BI, as important nucleus, are Astemizole (antihistaminic), Omeprazole (antiulcerative) and Rabendazole (fungicide), some of these compounds have the 2- aminobenzimidazole (2ABI) as base nucleus. The structure of 2ABI derivatives contains a cyclic guanidine moiety, which is interesting because of its free lone pairs, labile hydrogen atoms and planar delocalized structure. The delocalized 10-π electron system and the extension of the electron conjugation with the exocyclic amino group, in 2ABI, making these heterocycles to have amphoteric character. The 2ABI has been used as building blocks for the synthesis of several BI derivatives as medicinally important molecules. On these bases, herein, we present a bibliographic review concerning the recent methodologies used in the synthesis of 2ABIs, including the substituted ones.

scholarly journals Influence of Ultraviolet Radiation on Mechanical Properties of a Photoinitiator Compounded High Vinyl Styrene–Butadiene–Styrene Block Copolymer

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1287
Author(s):  
Sanjoy Datta ◽  
Radek Stocek ◽  
Kinsuk Naskar
Keyword(s):  
Mechanical Properties ◽  
Block Copolymer ◽  
Ultraviolet Radiation ◽  
Thermoplastic Elastomer ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
Time Saving ◽  
Styrene Butadiene Styrene ◽  
Styrene Butadiene ◽  
Butadiene Styrene

Ultraviolet curing of elastomers is a special curing technique that has gained importance over the conventional chemical crosslinking method, because the former process is faster, and thus, time-saving. Usually, a suitable photoinitiator is required to initiate the process. Ultraviolet radiation of required frequency and intensity excites the photoinitiator which abstracts labile hydrogen atoms from the polymer with the generation of free radicals. These radicals result in crosslinking of elastomers via radical–radical coupling. In the process, some photodegradation may also take place. In the present work, a high vinyl (~50%) styrene–butadiene–styrene (SBS) block copolymer which is a thermoplastic elastomer was used as the base polymer. An attempt was made to see the effect of ultraviolet radiation on the mechanical properties of the block copolymer. The process variables were time of exposure and photoinitiator concentration. Mechanical properties like tensile strength, elongation at break, modulus at different elongations and hardness of the irradiated samples were studied and compared with those of unirradiated ones. In this S-B-S block copolymer, a relatively low exposure time and low photoinitiator concentration were effective in obtaining optimized mechanical properties. Infrared spectroscopy, contact angle and scanning electron microscopy were used to characterize the results obtained from mechanical measurements.

scholarly journals Perdeuteration: Vital to visualising solvent in neutron crystallography?

2014 ◽  
Vol 70 (a1) ◽  
pp. C1208-C1208
Author(s):  
Stuart Fisher ◽  
Matthew Blakeley ◽  
Eduardo Howard ◽  
Isabelle Petit-Haertlein ◽  
Michael Haertlein ◽  
...  
Keyword(s):  
Water Molecules ◽  
Nuclear Density ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
High Quality ◽  
Density Maps ◽  
Unit Cells ◽  
Solvent Molecules ◽  
Neutron Protein Crystallography ◽  
Neutron Crystallography

Early neutron crystallography studies replaced hydrogen with deuterium by soaking the crystal in heavy water prior to data collection, which exchanged labile hydrogen atoms (OH, NH, and SH) and solvent molecules only. Carbon bonded hydrogen atoms were not replaced, and their negative scattering density resulted in cancellation in nuclear density maps with resolution worse than 1.8 Å. Furthermore complications arise due to partial exchange, where deuterium is present in some unit cells and hydrogen in others. More recently it has become possible to completely replace hydrogen with deuterium through expression in a deuterated medium, using facilities such as the Deuteration Laboratory (DLAB) in Grenoble. As this is a complex and expensive task, the question arises as to the importance of its use. As well as allowing the study of radically smaller crystals (<0.05mm3), it also has the possibility to avoid the cancellation problems discussed above. We have obtained data from high quality crystals of partially hydrogenated type III antifreeze protein, where methyl protonated valine and leucine residues were incorporated into the perdeuterated protein. This provides an excellent opportunity to assess the effects of negative scattering from hydrogen atoms not only on the visibility of neighbouring carbon atoms but also on water molecules in close vicinity. The observation of these cancellation effects gives a further reason to use full deuteration in neutron protein crystallography.

scholarly journals Quinone methide dimers lacking labile hydrogen atoms are surprisingly excellent radical-trapping antioxidants

2020 ◽  
Vol 11 (22) ◽  
pp. 5676-5689
Author(s):  
Mark A. R. Raycroft ◽  
Jean-Philippe R. Chauvin ◽  
Matthew S. Galliher ◽  
Kevin J. Romero ◽  
Corey R. J. Stephenson ◽  
...  
Keyword(s):  
Quinone Methide ◽  
Labile Hydrogen ◽  
Hydrogen Atoms ◽  
Radical Trapping ◽  
Synthetic Intermediates

Quinone method dimers, (bio)synthetic intermediates en route to many naturally products derived from resveratrol, are potent radical-trapping antioxidants, besting the phenols from which they are derived and to which they can be converted.

scholarly journals Hydrogen-Mediated Noncovalent Interactions in Solids: What Can NMR Crystallography Tell About?

Molecules ◽  
2020 ◽  
Vol 25 (16) ◽  
pp. 3757
Author(s):  
Ioana Georgeta Grosu ◽  
Xenia Filip ◽  
Maria O. Miclăuș ◽  
Claudiu Filip
Keyword(s):  
Crystal Engineering ◽  
Rational Design ◽  
Noncovalent Interactions ◽  
Molecular Crystals ◽  
Labile Hydrogen ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
Practical Applications ◽  
Comprehensive Picture ◽  
Nmr Crystallography

Hydrogen atoms play a crucial role in the aggregation of organic (bio)molecules through diverse number of noncovalent interactions that they mediate, such as electrostatic in proton transfer systems, hydrogen bonding, and CH–π interactions, to mention only the most prominent. To identify and adequately describe such low-energy interactions, increasingly sensitive methods have been developed over time, among which quantum chemical computations have witnessed impressive advances in recent years. For reaching the present state-of-the-art, computations had to rely on a pool of relevant experimental data, needed at least for validation, if not also for other purposes. In the case of molecular crystals, the best illustration for the synergy between computations and experiment is given by the so-called NMR crystallography approach. Originally designed to increase the confidence level in crystal structure determination of organic compounds from powders, NMR crystallography is able now to offer also a wealth of information regarding the noncovalent interactions that drive molecules to pack in a given crystalline pattern or another. This is particularly true for the noncovalent interactions which depend on the exact location of labile hydrogen atoms in the system: in such cases, NMR crystallography represents a valuable characterization tool, in some cases complementing even the standard single-crystal X-ray diffraction technique. A concise introduction in the field is made in this mini-review, which is aimed at providing a comprehensive picture with respect to the current accuracy level reached by NMR crystallography in the characterization of hydrogen-mediated noncovalent interactions in organic solids. Different types of practical applications are illustrated with the example of molecular crystals studied by our research group, but references to other representative developments reported in the literature are also made. By summarizing the major concepts and methodological progresses, the present work is also intended to be a guide to the practical potential of this relatively recent analytical tool for the scientists working in areas where crystal engineering represents the main approach for rational design of novel materials.

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