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

A refinement of the dickite structure and some remarks on polymorphism in kaolin minerals

1961 ◽  
Vol 32 (252) ◽  
pp. 683-704 ◽  
Author(s):  
Robert E. Newnham
Keyword(s):  
Crystal Structure ◽  
Absorption Spectra ◽  
Infrared Absorption ◽  
Structural Features ◽  
Mirror Image ◽  
Hydrogen Atoms ◽  
Octahedral Layer ◽  
Layer Structures ◽  
Infrared Absorption Spectra ◽  
Interlayer Bonding

SummaryThe crystal structure of the clay mineral dickite (Al2Si2H4O9) has been refined to a greater accuracy than that reported in an earlier analysis. Improved lattiçe parameters are: a 5·15±0·001, b 8·940±0·001, c 14·424 ± 0·002Å., β 96° 44′± 1′. The dickite structure shows several significant distortions from the geometry of the idealized kaolin layer, including deformation and rotation of the silica tetra-hedra. The most striking features of the octahedral layer are the extremely short shared edges of 2·37 Å. Although the analysis was not sufficiently accurate to position the hydrogen atoms with certainty, a model consistent with the infrared absorption spectra is proposed. The stacking sequences of kaolin-layer minerals have been considered with reference to the structural features observed in dickite. There are thirty-six ways of superposing two kaolin layers commensurate with the OH-O bonds found in kaolinite, dickite, and nacrite. The twelve sequences showing the least amount of cation-cation superposition between consecutive kaolin layers can be used to construct two one-layer cells, kaolinite and its mirror image, and twelve two-layer cells, including dickite and nacrite. The distortions of the kaolin layer introduce secondary variations in the interlayer bonding that suggest that dickite and nacrite are the most stable of the kaolin layer structures, since they possess the shortest oxygen-hydroxyl contacts.

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 The absorption spectrum of formic acid in the vacuum ultra-violet

1937 ◽  
Vol 162 (908) ◽  
pp. 110-120 ◽  
Keyword(s):  
Electronic Structure ◽  
Formic Acid ◽  
Absorption Spectra ◽  
Ultra Violet ◽  
The Body ◽  
Hydrogen Atoms ◽  
Absorption Bands ◽  
Additional Absorption ◽  
Lyman Continuum ◽  
Vacuum Ultra Violet

Absorption spectra in the far ultra-violet region of the spectrum have recently assumed an important role in fixing the electronic structures of polyatomic molecules. This has been especially true of organic molecules such as acetylene, ethylene, the alkyl halides, alcohols, ethers and ketones. While all “molecular electrons” (i. e. those not contained in inner shells) can be expected to give rise to absorption bands in the region 2000–1000 A, it most frequently happens that one special electron type dominates the absorption. For example, the excitation of non-bonding pπ electrons dominate the absorption of methyl and ethyl iodides (Price 1936 a ); so-called “lone pairs” located on the oxygen atoms are responsible for all the strong bands of water, formaldehyde, etc. (Mulliken 1935 a, b ; Price 1935 a , 1936 b ). In order to obtain discrete absorption bands, which are desirable for the purposes of interpreting electronic structure, it is usually necessary to take the very simplest organic molecule containing the group we wish to study. Thus for molecules of the type R 1 COO R 2 ( R being an alkyl group or a hydrogen atom) it has been found that only the simplest of these, namely formic acid, shows discrete absorption bands. The interpretation of the electronic structure of the carboxyl group will therefore depend to a considerable extent upon the analysis of these discrete bands. From the discussion which follows it will be easy to see why the continuous absorption from the larger molecules of the type R 1 COO R 2 follows roughly the envelope of the discrete absorption of HCOOH except in so far as it is enhanced in certain regions by additional absorption from C—C and C—H bonding electrons or suffers small shifts to longer wave-lengths as a result of the substitution of hydrogen atoms by alkyl groups. The experimental technique employed in obtaining absorption spectra in the vacuum ultra-violet has been described elsewhere (Collins and Price 1934). The Lyman continuum serves as the background against which the 19340. The Lyman continuum serves as the background against which the absorption is observed, and the gas under investigation is allowed to flow continuously through the body of the spectrograph.

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.

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