Structural isomerization of cyclopropane: a new mechanism through propylidene

1999 ◽  
pp. 1515-1516 ◽  
Author(s):  
Holger F. Bettinger ◽  
Jonathan C. Rienstra-Kiracofe ◽  
Brian C. Hoffman ◽  
Henry F. Schaefer III ◽  
Paul v. R. Schleyer ◽  
...  
Keyword(s):  
Structural Isomerization

Multiple Stimuli Triggered Structural Isomerization of Copper Iodide-pyridine Crystals

CrystEngComm ◽  
2021 ◽  
Author(s):  
Quanxiang Han ◽  
Xin Ye ◽  
Xiaoxin Zheng ◽  
Qing Guo ◽  
Qinglian Lin ◽  
...  
Keyword(s):  
Chemical Properties ◽  
Copper Iodide ◽  
Physico Chemical ◽  
Structural Isomerization ◽  
External Stimuli

Copper based coordination materials possess the ability to exhibit changes of their physico-chemical properties in response to external stimuli. Recent researches related to Cu(I) complexes have revealed the external stimuli...

scholarly journals Design, Synthesis, and In Vitro Evaluation of Hydroxybenzimidazole-Donepezil Analogues as Multitarget-Directed Ligands for the Treatment of Alzheimer’s Disease

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 985 ◽  
Author(s):  
Sílvia Chaves ◽  
Simonetta Resta ◽  
Federica Rinaldo ◽  
Marina Costa ◽  
Romane Josselin ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Neuroblastoma Cells ◽  
Biological Properties ◽  
Design Synthesis ◽  
Aβ Aggregation ◽  
Structural Isomerization ◽  
Good Potential ◽  
Nitro Derivatives

A series of multi-target-directed ligands (MTDLs), obtained by attachment of a hydroxyphenylbenzimidazole (BIM) unit to donepezil (DNP) active mimetic moiety (benzyl-piperidine/-piperazine) was designed, synthesized, and evaluated as potential anti-Alzheimer’s disease (AD) drugs in terms of biological activity (inhibition of acetylcholinesterase (AChE) and β–amyloid (Aβ) aggregation), metal chelation, and neuroprotection capacity. Among the DNP-BIM hybrids studied herein, the structural isomerization did not significantly improve the biological properties, while some substitutions, namely fluorine atom in each moiety or the methoxy group in the benzyl ring, evidenced higher cholinergic AChE activity. All the compounds are able to chelate Cu and Zn metal ions through their bidentate BIM moieties, but compound 5, containing a three-dentate chelating unit, is the strongest Cu(II) chelator. Concerning the viability on neuroblastoma cells, compounds 9 and 10 displayed the highest reduction of Aβ-induced cell toxicity. In silico calculations of some pharmacokinetic descriptors indicate that all the compounds but the nitro derivatives have good potential oral-bioavailability. Overall, it can be concluded that most of the studied DNP-BIM conjugates showed quite good anti-AD properties, therefore deserving to be considered in further studies with the aim of understanding and treating AD.

Zwitterion formation and subsequent carboxylate–pyridinium NH synthon generation through isomerization of 2-anilinonicotinic acid

CrystEngComm ◽  
2018 ◽  
Vol 20 (40) ◽  
pp. 6126-6132
Author(s):  
Pengyun Yue ◽  
Caiqiao Dong ◽  
Mingtao Zhang ◽  
Danrui Xu ◽  
Sean Parkin ◽  
...  
Keyword(s):  
Solid State ◽  
Structural Isomerization ◽  
Zwitterion Formation

Structural isomerization of 2-anilinonicotinic acids to 4-anilinonicotinic acids leads to an increase of ΔpKa, thus leading to the formation of a carboxylate–pyridinium NH dimer in the solid state.

Structural Isomerization of the Gas-Phase 2-Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

2014 ◽  
Vol 53 (23) ◽  
pp. 5888-5891 ◽  
Author(s):  
Jonathan D. Mosley ◽  
Justin W. Young ◽  
Jay Agarwal ◽  
Henry F. Schaefer ◽  
Paul v. R. Schleyer ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Computational Chemistry ◽  
Gas Phase ◽  
Phase 2 ◽  
Structural Isomerization

Structural isomerization allene .dblarw. propyne. Studies with a single pulse shock tube

1975 ◽  
Vol 79 (12) ◽  
pp. 1148-1152 ◽  
Author(s):  
Assa Lifshitz ◽  
Michael Frenklach ◽  
Alexander Burcat
Keyword(s):  
Shock Tube ◽  
Single Pulse ◽  
Structural Isomerization

SINGLET METHYLENE FROM THERMAL DECOMPOSITION OF DIAZOMETHANE. UNIMOLECULAR REACTIONS OF CHEMICALLY ACTIVATED CYCLOPROPANE AND DIMETHYLCYCLOPROPANE MOLECULES

1962 ◽  
Vol 40 (7) ◽  
pp. 1425-1451 ◽  
Author(s):  
D. W. Setser ◽  
B. S. Rabinovitch
Keyword(s):  
Thermal Decomposition ◽  
Rate Constants ◽  
Vibrational Energy ◽  
Kcal Mole ◽  
Thermal Systems ◽  
Geometric Isomerization ◽  
Wide Range ◽  
Structural Isomerization ◽  
Quantum Statistical ◽  
Singlet Methylene

The thermal decomposition of diazomethane (DM) into singlet methylene radicals and nitrogen has been studied from 225° to 450° in 10:1 olefin–diazomethane mixtures. At 2.5 cm pressure, k = 1.2 × 1012 exp (−34,000/RT) sec−1. The methylene radicals have similar reactivity to methylene generated from photolytic decomposition of DM, as judged by the follow-up reactions with ethylene and cis-butene-2. The structural isomerization reactions of energized cyclopropane and the structural and geometric isomerization of 1,2-dimethyl-cyclopropane (DMC), formed from the addition of the thermally generated methylene to the olefins, were measured from 250° to 450° over a wide range of pressures. For comparison, cyclopropane formed from photolysis at 4358 Å and 25° of DM and ethylene was studied. As judged from comparison of the experimental isomerization rate constants, the energy of the cyclopropanes formed at 350° in the thermal DM system is about the same as for cyclopropanes formed by photolysis at 4358 Å of DM at 25°. The experimental rate constants obtained on the assumption of strong collisions are compared with calculated rate constants which are based on quantum statistical models for kE which fit literature data on conventional thermal isomerization of cyclopropane and DMC. From this comparison, the average energies of the formed molecules in the thermal systems are estimated to be between 107 and 115 kcal/mole, depending upon the temperature. Photolysis at 25° of the ketene–ethylene system (3200 Å) and of DM–ethylene system (4358 Å) give cyclopropane characterized as being at 103 and 111 kcal/mole respectively. These energies deduced from kinetic data are compared with available thermochemical quantities; the existing value of ΔHf0(CH2N2) is questioned. Further support for fast intramolecular relaxation of vibrational energy in DMC, relative to the relaxation process for reaction, is noted. Comparison of data in the literature on the ketene and DM photolytic systems strongly suggests that a larger fraction of the excess light energy resides with methylene from ketene (0.65–0.8) than with methylene from DM (0.3–0.5). Various approximations for the calculation of kE are examined and are compared with accurate quantum statistical evaluation.

The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes

1985 ◽  
Vol 63 (7) ◽  
pp. 1424-1430 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers
Keyword(s):  
Ground State ◽  
Internal Conversion ◽  
Rydberg State ◽  
Singlet State ◽  
Hydrogen Shift ◽  
Geometric Isomerization ◽  
Trans Isomerization ◽  
Show Evidence ◽  
Structural Isomerization ◽  
Π State

We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.

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