scholarly journals Benzazole derivatives: V. The reactivity of some 2-p-tolyl-and 2-p-methylstyryl-benzimidazolium salts

2004 ◽  
Vol 58 (12) ◽  
pp. 548-551
Author(s):  
Corina Cernatescu ◽  
Eugenia Comanita
Keyword(s):  
Aromatic Aldehydes ◽  
The Other ◽  
Steric Effects ◽  
Methyl Group ◽  
Condensation Reactions ◽  
Other Hand ◽  
Benzimidazolium Salts

The reactivity of the p-substituted methyl group in 1-methyl-2-p-tolylbenzimidazolium and 1-methyl-2-p-methylstyrylbenzimidazolium iodides with p-nitroso-dimethylaniline (p-NDMA) and aromatic aldehydes was studied. According to literature data on the steric effects produced by the bulky N-l methyl group, the 2-p-tolyl substituted salt does not react with p-NDMA. On the other hand, 2-p-methylstyryl substituted salts give condensation reactions, similarly to 1,2,3-trimethylbenzimidazolium iodides. The compounds obtained from the reaction with aromatic aldehydes can be used as dyeing substances, photosensitizers or as dienic monomers, due to the conjugated chain from C-2.

scholarly journals Diaqua(nitrato-κ2O,O′)bis(L-valine-κO)lead(II) nitrate at 296 K

IUCrData ◽  
2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Sylvain Bernès ◽  
Laura Gasque
Keyword(s):  
Low Temperature ◽  
Bond Length ◽  
Coordination Number ◽  
Coordination Sphere ◽  
Title Complex ◽  
The Other ◽  
Methyl Group ◽  
Space Group ◽  
Polymeric Nature ◽  
Other Hand

The structure of the title complex, [Pb(NO3)(C5H11NO2)2(H2O)2]NO3, had been determined previously at 173 and 193 K, and is now reported at 296 K, in the same space group. The main difference with the low-temperature structures is that a methyl group of one valine ligand is clearly disordered over two positions, for which the occupancies converged to 0.56 (3) and 0.44 (3). Bond-length variations within the coordination sphere of PbIIas a function ofTare difficult to assess because uncertainties on these parameters are high. On the other hand, Pb...O distances above 2.9 Å cannot be assigned unambiguously to formal Pb—O bonds. As a consequence, the polymeric nature of the complex previously described at 173 K is uncertain, as well as the actual coordination number of PbII, and it is thus not possible to determine if the metal environment is holo- or hemidirected.

STEROIDS AND RELATED PRODUCTS: VII. THE SYNTHESIS OF 17α-METHYLCORTICOSTERONE

1957 ◽  
Vol 35 (2) ◽  
pp. 131-140 ◽  
Author(s):  
Ch. R. Engel
Keyword(s):  
Ethylene Glycol ◽  
Biologically Active ◽  
The Other ◽  
Keto Group ◽  
Methyl Group ◽  
Other Hand ◽  
Hydrolysis Of

The synthesis of 17α-methylcorticosterone, a new biologically active homologue of corticosterone and analogue of cortisol, is described. In the course of the work it was observed that the 17-methyl group greatly impeded both the formation and the hydrolysis of a 20-ketal. On the other hand, evidence was obtained that the 11-keto group is not completely unreactive towards ethylene glycol, in the presence of p-toluenesulphonic acid.

Steric activation in prototropic reactions of pyrazine derivatives. II. The Brønsted relation

1986 ◽  
Vol 64 (6) ◽  
pp. 1090-1092 ◽  
Author(s):  
K. Nagarajan ◽  
T. W. S. Lee ◽  
R. R. Perkins ◽  
Ross Stewart
Keyword(s):  
Transition State ◽  
The Other ◽  
Steric Effects ◽  
Methyl Groups ◽  
Reaction Centre ◽  
Organic Electrolytes ◽  
Methyl Group ◽  
Pyridine Bases ◽  
Tentative Explanation ◽  
High Concentrations

The rate of deprotonation of the 2-methyl group in 1,2,3-trimethylpyrazinium ion by carboxylate, aniline, and pyridine bases has been measured in D2O. Carboxylate ions containing bulky groups near the reaction centre, e.g. ortho benzoates, react faster than predicted by the Brønsted equation that correlates the reactions of unhindered carboxylates. Anilines and pyridines, on the other hand, show conventional steric effects. A tentative explanation for the activation engendered by groups adjacent to the carboxylate centre is based on the known effect that high concentrations of organic electrolytes have on the strengths of carboxylic acids but not of amines. Since ortho carboxylate ions have their relative basicities increased by an alkyl-rich environment, it is argued that the reactive methyl groups of the substrate might provide such an interaction in the transition state.

Stereochemistry of bimolecular nucleophilic opening of a dioxolenium ring fused to an anchored cyclohexane system

1969 ◽  
Vol 47 (9) ◽  
pp. 1445-1459 ◽  
Author(s):  
J. F. King ◽  
A. D. Allbutt
Keyword(s):  
Transition States ◽  
Heterocyclic Ring ◽  
The Other ◽  
Cyclohexane Ring ◽  
Methyl Group ◽  
Other Hand ◽  
Opening Ratio ◽  
Nucleophilic Reagents

This paper describes the characterization of certain dioxolenium salts in which the heterocyclic ring is fused (via positions-4 and -5) to an anchored cyclohexane ring, and the steric course of their bimolecular cleavage with nucleophilic reagents. It was found that diaxial opening is normally favored strongly over diequatorial; this is accounted for in terms of differences in angle strain in the transition states. The presence of an axial (angular) methyl group gave a preference for diequatorial opening; on the other hand an analogous investigation of the diaxial: diequatorial opening ratio with epoxides showed the stereochemistry of the reaction to be virtually insensitive to an angular methyl group. These observations are interpreted in terms of the different non-bonded interactions arising from the different geometrical arrangements of epoxides and dioxolenium ions. The variation in the diaxial: diequatorial opening ratio is shown to be of significance in the interpretation of rates of diaxial → diequatorial rearrangement.

scholarly journals Four-component reaction of cyclic amines, 2-aminobenzothiazole, aromatic aldehydes and acetylenedicarboxylate

2013 ◽  
Vol 9 ◽  
pp. 2934-2939 ◽  
Author(s):  
Hong Gao ◽  
Jing Sun ◽  
Chao-Guo Yan
Keyword(s):  
Aromatic Aldehydes ◽  
The Other ◽  
Cyclic Amines ◽  
Toluenesulfonic Acid ◽  
Other Hand

The four-component reaction of 2-aminobenzothiazole, aromatic aldehydes, acetylenedicarboxylate and piperidine or pyrrolidine in ethanol afforded the functionalized 2-pyrrolidinones containing both benzothiazolyl and piperidinyl (or pyrrolidinyl) units in good yields. On the other hand, the similar four-component reactions resulted in the functionalized morpholinium or piperidinium 2-pyrrolidinon-3-olates in the presence of p-toluenesulfonic acid.

scholarly journals Versatile Coordination Polymer Catalyst for Acid Reactions Involving Biobased Heterocyclic Chemicals

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 190
Author(s):  
Margarida M. Antunes ◽  
Ricardo F. Mendes ◽  
Filipe A. Almeida Paz ◽  
Anabela A. Valente
Keyword(s):  
Coordination Polymer ◽  
Metal Organic Framework ◽  
Aromatic Aldehydes ◽  
Catalytic Reactions ◽  
The Other ◽  
Biomass Pyrolysis ◽  
Other Hand ◽  
Polymer Catalyst ◽  
Metal Organic ◽  
Acid Catalyzed

The chemical valorization/repurposing of biomass-derived chemicals contributes to a biobased economy. Furfural (Fur) is a recognized platform chemical produced from renewable lignocellulosic biomass, and furfuryl alcohol (FA) is its most important application. The aromatic aldehydes Fur and benzaldehyde (Bza) are commonly found in the slate of compounds produced via biomass pyrolysis. On the other hand, glycerol (Gly) is a by-product of the industrial production of biodiesel, derived from fatty acid components of biomass. This work focuses on acid catalyzed routes of Fur, Bza, Gly and FA, using a versatile crystalline lamellar coordination polymer catalyst, namely [Gd(H4nmp)(H2O)2]Cl·2H2O (1) [H6nmp=nitrilotris(methylenephosphonic acid)] synthesized via an ecofriendly, relatively fast, mild microwave-assisted approach (in water, 70 °C/40 min). This is the first among crystalline coordination polymers or metal-organic framework type materials studied for the Fur/Gly and Bza/Gly reactions, giving heterobicyclic products of the type dioxolane and dioxane, and was also effective for the FA/ethanol reaction. 1 was stable and promoted the target catalytic reactions, selectively leading to heterobicyclic dioxane and dioxolane type products in the Fur/Gly and Bza/Gly reactions (up to 91% and 95% total yields respectively, at 90 °C/4 h), and, on the other hand, 2-(ethoxymethyl)furan and ethyl levulinate from heterocyclic FA.

scholarly journals Benzoin condensation of aromatic aldehydes catalyzed by N-heterocyclic carbenes under mild conditions

2019 ◽  
Vol 10 (1) ◽  
pp. 1-6
Author(s):  
Isabel Monreal-Leyva ◽  
Breanna Rose Attema ◽  
Nuri Bae ◽  
Haishi Cao ◽  
Hector Palencia
Keyword(s):  
Alkyl Substituent ◽  
Aromatic Aldehydes ◽  
Heterocyclic Carbenes ◽  
The Other ◽  
Steric Effects ◽  
Reaction Yield ◽  
Electronic Effects ◽  
Mild Conditions ◽  
Benzoin Condensation

The benzoin condensation was used to evaluate the catalytic activity of different N-heterocyclic carbenes as a function of their structure and N-substituents. There is a correlation between the length of an N-alkyl substituent and its performance as an organocatalyst. Heteroaromatic aldehydes were found to be the most reactive, among the screened substrates, finishing the reaction in 30 minutes, with almost quantitative yields. On the other hand, p-nitrobenzaldehyde, a strongly electrophilic aldehyde, was the least reactive. Electronic effects have little influence on the reaction yield but steric effects can dramatically reduce it. The preformed organocatalyst reacts faster than the generated in situ, with minimum solvent.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

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