Synthesis of Ni/NiAlOx Catalysts for Hydrogenation Saturation of Phenanthrene

The saturation of octahydrophenanthrene was the rate-determining step in the hydrogenation process from phenanthrene to perhydrophenanthrene, which was due to the steric hindrance and competitive adsorption of octahydrophenanthrene. In this work, a series of Ni/NiAlOx catalysts with a uniform electron-deficient state of Ni derived from the nickel aluminate structure was synthesized to overcome the disadvantage of noble catalyst and the traditional sulfided catalysts in the saturation hydrogenation process of phenanthrene. Results showed that the catalyst calcinated at 650°C possessed more Ni2+ (∼98%) occupying octahedral sites and exhibited the highest robs (1.53 × 10−3 mol kg−1 s−1) and TOF (14.64 × 10−3 s−1) for phenanthrene hydrogenation. Furthermore, its ability to overcome steric hindrance and promote the rate-determining step was proven by octahydrophenanthrene hydrogenation. Comparing the evolution of hydrogenation activity with the change in the electronic structure of surface Ni sites, it was shown that the increase of metallic electron deficiency hindered the π-back bonding between surface Ni and aromatic rings, which was unfavorable for aromatic adsorption. As a result, the phenanthrene hydrogenation saturation performance can be enhanced by stabilizing the electron-deficient state of surface Ni on an optimal degree.

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Molekülinterne Dipolorientierung und dielektrische Absorption in verdünnter Lösung bei Mikro-und Submillimeterwellen. V.Acetyl-Verbindungen

Zeitschrift für Naturforschung A ◽

10.1515/zna-1989-0914 ◽

1989 ◽

Vol 44 (9) ◽

pp. 853-865

Author(s):

Gerhard Klages

Keyword(s):

Fourier Transform ◽

Dielectric Loss ◽

Steric Hindrance ◽

Loss Factor ◽

The Other ◽

Fourier Transform Spectrometer ◽

Aromatic Rings ◽

Molecular Laser ◽

Aliphatic Compounds ◽

Fast Relaxation

Abstract The dielectric loss of sixteen molecules, eleven with the acetyle group in aromatic bonds and five in aliphatic bonds, has been measured in very dilute solutions of cyclohexene at 20 °C. Five of these molecules are investigated in decalene solutions, too. The measurements have been made at wavenumbers in the range 0.08 to 140 cm -1 above 8 cm -1 making use of a pumped molecular laser. They are supplemented by the data of a Fourier transform spectrometer up to 300 cm -1. All microwave spectra of loss factor ε″ are analysed in terms of three absorption areas using the two variable Mori formalism. On the other hand, Lorentz curves are fitted to the FIR absorption spectra of α(v̄).The fast relaxation process of the aliphatic compounds is suggested to be due to intramolecular reorientation of the acetyle group itself, since in acetyle cyclohexene the remaining part of the molecule is rigid. To the contrary, the acetyle group is not able to reorientate swiftly, if bounded to aromatic rings. Presumably, it is fixed by mesomeric interaction with the dipole in the plain of the ring. However, 2-methyl acetophenone and 1-acetyle naphthone show some quick dipole reorientation, which coincides with a steric hindrance of the group in entering the plain of the ring.

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Multiple changes in rate-determining step in the acid and base catalyzed cyclizations of ethyl N-(p-nitrophenyl)hydantoates caused by methyl substitution

Canadian Journal of Chemistry ◽

10.1139/v99-079 ◽

1999 ◽

Vol 77 (5-6) ◽

pp. 849-859

Author(s):

Iva B Blagoeva ◽

Anthony J Kirby ◽

Asen H Koedjikov ◽

Ivan G Pojarlieff

Keyword(s):

Steric Hindrance ◽

Acid Catalysis ◽

Isotope Effects ◽

Base Catalysis ◽

Ethoxy Group ◽

First Order ◽

Tetrahedral Intermediate ◽

General Base ◽

Rate Determining Step ◽

Acid And Base

The slopes of the pH-rate profiles for the cyclization of 2-methyl- and 2,3-dimethyl hydantoates 1-NPU and 2-NPU between pH 1 and 7 change from 1 to 0 and then back to 1. A reaction first order in H+ was observed with the latter compound. The 2,2,3-trimethyl derivative 3-NPU showed only one reaction first order in OH-, but complex acid catalysis is described by slopes 0, -1, 0, and finally -1 again. The cyclizations were general base catalyzed, with Brønsted β values of 0.5-0.6. The OH- catalysis at higher pH for 1-NPU and 2-NPU showed inverse solvent kinetic isotope effects and deviated from the Brønsted relationships, while that for 3-NPU showed a normal effect and complied with the Brønsted relationship. The accelerations due to the gem-dimethyl effect were lost with the OH- and general base-catalyzed reactions of 3-NPU. This behaviour is due to a change from the rate-determining formation of the tetrahedral intermediate with 1-NPU and 2-NPU to the rate-determining breakdown with 3-NPU, due to steric hindrance to protonation of the leaving ethoxy group. The OH- reaction at higher pH involves attack of the ureide anion with 1-NPU and 2- NPU, becoming concerted with deprotonation when catalyzed by general bases and changing to acid inhibition of the anion of the tetrahedral intermediate at low pH. With 3-NPU at higher pH, T- is in equilibrium and the conjugate acids of the general bases accelerate its breakdown by protonating the ethoxy group. Acid catalysis of the cyclization of 3-NPU at higher pH is also protonation of the leaving group from T0 changing to the rate-determining formation of T at lower pH. The latter mechanism is preferred for the cyclization of 2-NPU.Key words: gem-dimethyl effect, mechanism, general base catalysis, proton transfer, steric hindrance.

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ESIPT-AIE active Schiff base based on 2-(2′-hydroxyphenyl)benzo-thiazole applied as multi-functional fluorescent chemosensors

Dalton Transactions ◽

10.1039/d1dt00241d ◽

2021 ◽

Author(s):

Han-Wen Zheng ◽

Yang Kang ◽

Min Wu ◽

Qiong-Fang Liang ◽

Jian-Quan Zheng ◽

...

Keyword(s):

Schiff Base ◽

Metal Ions ◽

Steric Hindrance ◽

Fluorescent Chemosensors ◽

Aromatic Rings ◽

Active Compounds

For AIE-ESIPT-active compounds, their steric hindrance, rotatable aromatic rings and isomerism should be considered when sensing metal ions.

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Crystal structure of methyl 2-[2,4-bis(4-fluorophenyl)-3-azabicyclo[3.3.1]nonan-9-ylidene]hydrazinecarboxylate

Acta Crystallographica Section E Structure Reports Online ◽

10.1107/s1600536814018935 ◽

2014 ◽

Vol 70 (9) ◽

pp. 145-147

Author(s):

A. Kamaraj ◽

R. Rajkumar ◽

K. Krishnasamy ◽

S. Murugavel

Keyword(s):

Crystal Structure ◽

Hydrogen Bonding ◽

Hydrogen Bonds ◽

Steric Hindrance ◽

Pyridine Ring ◽

Chair Conformation ◽

Ring System ◽

Aromatic Rings ◽

Compound C ◽

Supramolecular Chains

In the title compound, C22H23F2N3O2, the bicyclic ring system exists in a twin-chair conformation with an equatorial disposition of the 4-fluorophenyl groups on the heterocycle. These aromatic rings are inclined to one another by 19.4 (1)°. In the crystal, molecules are linked by pairs of N—H...O and C—H...O hydrogen bonds into inversion dimers, incorporatingR12(7) andR22(8) ring motifs; the same O atom accepts both hydrogen bonds. These dimers are further linked by a pair of C—H...F hydrogen bonds, enclosingR22(28) ring motifs, forming supramolecular chains along [010]. The NH group of the pyridine ring is not involved in hydrogen bonding, probably due to the steric hindrance of the fluorophenyl groups.

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THE KINETICS OF REACTION OF 2,2-DIPHENYL-1-PICRYLHYDRAZYL WITH PHENOLS

Canadian Journal of Chemistry ◽

10.1139/v61-202 ◽

1961 ◽

Vol 39 (8) ◽

pp. 1588-1594 ◽

Cited By ~ 70

Author(s):

J. S. Hogg ◽

D. H. Lohmann ◽

K. E. Russell

Keyword(s):

Hydrogen Atom ◽

Steric Hindrance ◽

Hydrogen Abstraction ◽

Phenoxy Radical ◽

First Order ◽

Rate Determining Step ◽

Kinetics Of Reaction ◽

Kinetics Of

The kinetics of reaction between 2,2-diphenyl-1-picrylhydrazyl (DPPH) and a wide variety of phenols have been studied. The rate of disappearance of DPPH is of first order with respect to both the DPPH and the reacting phenol. The rates of reaction can be roughly correlated with the Hammett σ value of the phenol substituent in the range −0.4 < σ < 0.2, a ρ value of −6 being obtained. t-Butyl groups in both ortho positions of the phenol give rise to steric hindrance, the reduction in rate being largely due to a reduction in the A factor. Hydrogen abstraction from the less reactive phenols is strongly retarded by the product, 2,2-diphenyl-1-picrylhydrazine.The rate-determining step probably involves the abstraction of a hydrogen atom from the phenol by the DPPH to give diphenylpicrylhydrazine and a phenoxy radical. The retardation by diphenylpicrylhydrazine is readily explained if this primary step is reversible.

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Kinetics of Z–E isomerization of spiroindolinopyrans

Canadian Journal of Chemistry ◽

10.1139/v78-215 ◽

1978 ◽

Vol 56 (9) ◽

pp. 1296-1301 ◽

Cited By ~ 6

Author(s):

Ilona Gruda ◽

Roger M. Leblanc ◽

Jerzy Sochanski

Keyword(s):

Steric Hindrance ◽

Polar Solvents ◽

Rate Determining Step ◽

Nonpolar Solvents ◽

Protic Solvents ◽

Kinetics Of

The kinetics of the Z–E isomerization of a series of 3′-nonsymmetrically substituted spiroindolinopyrans bas been studied by nmr in different solvents.The rate-determining step in nonpolar solvents was found to be the cleavage of the C—O bond whereas in polar solvents it was the C(2)—C(3) bond rotation.A strong steric hindrance of substituents at carbon 3 was observed. It was found that the rate of the isomerization is more sensitive to the bulkiness of the substituent at C(3′) than at the N(1′). Protic solvents enhance the reaction more than nonprotic polar solvents.

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Competitive Adsorption of Xylene and Toluene on Modified and Unmodified Sodium Bentonite Clay Mineral

Asian Journal of Applied Chemistry Research ◽

10.9734/ajacr/2020/v5i230143 ◽

2020 ◽

pp. 68-80

Author(s):

H. E. Ewuzie ◽

T. N. Chikwe ◽

N. C. Ngobiri ◽

I. P. Okoye

Keyword(s):

Competitive Adsorption ◽

High Capacity ◽

Bentonite Clay ◽

Test Results ◽

Sodium Bentonite ◽

Rate Determining Step ◽

Swelling Capacity ◽

Aqueous Effluents ◽

Pseudo Second Order ◽

Ft Ir

Cetyltrimethylammonium bromide (CTAB) – modified and unmodified sodium bentonite were both used for the competitive adsorption of m-xylene and toluene from their aqueous solution. Infrared spectroscopy (IR) and expansion tests (adsorption capacity and Foster swelling) measurement were performed in order to evaluate the performance of the adsorbents. The FT-IR results indicated that the quaternary ammonium salts (CTAB) were intercalated between the layers of the sodium bentonite clay. The Foster swelling test results indicated that the affinity of CTAB was more in the treated clay for all other organic compounds tested. The result showed that modified sodium bentonite swelled more than the unmodified and the order of the swelling factor is; m- xylene > toluene > gasoline > diesel > kerosene > water. However, when the assay was performed under agitation, it yielded higher swelling capacity. The modified clay exhibited very high capacity of adsorption compare to unmodified samples. The m-xylene and toluene uptake follows a pseudo second order kinetics mechanism, suggesting that the rate determining step of adsorption involves the two adsorbates competitively adsorbed on the adsorbent sites. Therefore this organo-modified bentonite can be used for the removal of organics from polluted aqueous effluents.

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A New Example of Edge-to-Face Interaction of Aromatic Rings in Oligopeptides: Cyclolinopeptide A

Zeitschrift für Naturforschung B ◽

10.1515/znb-1990-0916 ◽

1990 ◽

Vol 45 (9) ◽

pp. 1324-1326 ◽

Cited By ~ 7

Author(s):

Ignacy Z. Siemion

Keyword(s):

Steric Hindrance ◽

Nmr Spectra ◽

Side Chains ◽

Free Rotation ◽

Aromatic Rings ◽

Aromatic Residues ◽

Face Pair ◽

Aromatic Region ◽

C Nmr

The analysis of the aromatic region of 1H and 13C NMR spectra of cyclolinopeptide A (cyclic nonapeptide with the sequence c—(Pro— Pro— Phe—Phe—Leu— Ile— Ile— Leu— Val— ), (CLA)) shows that Phe-3 and Phe-4 aromatic rings are oriented nearly perpendicularly to each other, forming edge-to-face pair. It signifies the strong limitation of the free rotation of aromatic residues, probably because of the steric hindrance exerted by proximal aliphatic side chains of CLA.

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Chemical and orientational imaging of polymeric samples

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168074 ◽

1994 ◽

Vol 52 ◽

pp. 68-69

Author(s):

H. Ade ◽

B. Hsiao ◽

G. Mitchell ◽

E. Rightor ◽

A. P. Smith ◽

...

Keyword(s):

Ethylene Terephthalate ◽

National Laboratory ◽

Brookhaven National Laboratory ◽

Carbonyl Groups ◽

Aromatic Rings ◽

Edge Structure ◽

X Ray ◽

Scanning Transmission ◽

Polymeric Samples ◽

X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

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