scholarly journals Regiodivergent C−H and Decarboxylative C−C Alkylation by Ruthenium Catalysis: ortho versus meta Position‐Selectivity

2020 ◽  
Vol 59 (42) ◽  
pp. 18795-18803 ◽  
Author(s):  
Korkit Korvorapun ◽  
Marc Moselage ◽  
Julia Struwe ◽  
Torben Rogge ◽  
Antonis M. Messinis ◽  
...  
Keyword(s):  
Meta Position ◽  
Ruthenium Catalysis

Perturbation theory of substituent effect. Importance of the field effect in transmission of the substituent effect

1980 ◽  
Vol 45 (6) ◽  
pp. 1655-1661 ◽  
Author(s):  
Robert Ponec
Keyword(s):  
Perturbation Theory ◽  
Carboxylic Acids ◽  
Quantum Chemical ◽  
Substituent Effect ◽  
Field Effect ◽  
Adequate Description ◽  
Meta Position ◽  
Unsaturated Carboxylic Acids

Various quantum chemical approaches to the problem of transmission of the substituent effect were compared. It was shown that inclusion of the electronic repulsion (field effect) was necessary to give a true picture of differences in ρ constants for reactions of the cis and trans isomers of substituted unsaturated carboxylic acids; the same holds for an adequate description of transmission of the substituent effect from the meta position on a given skeleton.

scholarly journals Optical investigations and photoactive solar energy applications of new synthesized Schiff base liquid crystal derivatives

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fowzia S. Alamro ◽  
Sobhi M. Gomha ◽  
Mohamed Shaban ◽  
Abeer S. Altowyan ◽  
Tariq Z. Abolibda ◽  
...  
Keyword(s):  
Solar Energy ◽  
Liquid Crystalline ◽  
Molecular Structures ◽  
Light Illumination ◽  
Electrical Measurements ◽  
Scanning Calorimetry ◽  
Energy Applications ◽  
Meta Position ◽  
Chain Group ◽  
Liquid Crystalline Materials

AbstractNew homologues series of liquid crystalline materials namely, (E)-3-methoxy-4-[(p-tolylimino)methyl]phenyl 4-alkloxybenzoates (I-n), were designed and evaluated for their mesomorphic and optical behavior. The prepared series constitutes three members that differ from each other by the terminally attached alkoxy chain group, these vary between 6 and 12 carbons. A laterally OCH3 group is incorporated into the central benzene ring in meta position with respect to the ester moiety. Mesomorphic characterizations of the prepared derivatives are conducted using differential scanning-calorimetry (DSC), polarized optical-microscopy (POM). Molecular structures were elucidated by elemental analyses and NMR spectroscopy. DSC and POM investigations revealed that all the synthesized derivatives are purely nematogenic exhibiting only nematic (N) mesophase, except for the longest chain derivative (I-12) that is dimorphic possesses smectic A and N phases. Moreover, all members of the group have a wide mesomorphic range with high thermal nematic stability. A comparative study was established between the present derivative (I-6) and their previously prepared isomer. The results indicated that the location exchange of the polar compact group (CH3) influences the N mesophase stability and range. The electrical measurements revealed that all synthesized series I-n show Ohmic behaviors with effective electric resistances in the GΩ range. Under white light illumination, the effective electric conductivity for the compound I-8 is five times that obtained in dark conditions. This derivative also showed two direct optical band gaps in the UV and visible light range. In addition, I-6 has band energy gaps of values 1.07 and 2.79 eV, which are suitable for solar energy applications.

Strongly hindered rotation in α,α,2,6-terrachlorotoluene. Stereospecific five-bond coupling. Hyperconjugative contributions to long-range sidechain-ring proton coupling constants

1968 ◽  
Vol 46 (12) ◽  
pp. 2187-2188 ◽  
Author(s):  
T. Schaefer ◽  
R. Schwenk ◽  
C. J. Macdonald ◽  
W. F. Reynolds
Keyword(s):  
Free Energy ◽  
Resonance Spectrum ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
Ring Proton ◽  
Meta Position ◽  
Proton Coupling ◽  
Free Energy Of Activation

At −40 °C the C—H bond of the dichloromethyl group of α,α,2,6-tetrachlorotoluene lies in the plane of the ring. The proton resonance spectrum demonstrates a stereospecific five-bond coupling between the C—H proton and the ring proton in the meta position. The coupling to the para proton is essentially zero as expected from a hyperconjugative mechanism. The free energy of activation of rotation of the dichloromethyl group is about 15 kcal/mole at 25 °C.

Remote C–H Functionalizations by Ruthenium Catalysis

Synthesis ◽  
2021 ◽  
Author(s):  
Korkit Korvorapun ◽  
Ramesh C. Samanta ◽  
Torben Rogge ◽  
Lutz Ackermann
Keyword(s):  
Steric Hindrance ◽  
Late Stage ◽  
Crop Protection ◽  
Full Control ◽  
Site Selectivity ◽  
Important Approach ◽  
Distinct Character ◽  
Ruthenium Catalysis ◽  
Material Sciences ◽  
Site Selective

Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we highlight important mechanistic insights by experiments and computation, highlighting the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.

Nucleophilic addition to di- and poly-iron arene complex cations

1996 ◽  
Vol 74 (11) ◽  
pp. 2073-2082 ◽  
Author(s):  
Alaa S. Abd-Ei-Aziz ◽  
Debbie A. Armstrong ◽  
Shelly Bernardin ◽  
Harold M. Hutton
Keyword(s):  
Nucleophilic Addition ◽  
Iron Complexes ◽  
Iron Complex ◽  
Cyanide Anion ◽  
Meta Position ◽  
Arene Complex ◽  
Nmr Techniques ◽  
Cyano Groups ◽  
Predominant Effect

Hydride and cyanide addition to a series of di- and polycyclopentadienyliron arene complex cations with etheric bridges is described. Reaction of the di-iron complexes with sodium borohydride resulted in the formation of a number of adducts.p-Methyl- and o,o-dimethylphenoxybenzene cyclopentadienyliron complexes were used as models in this study to allow for the characterization of the analagous di-iron complexes. The use of HH COSY and CH COSY NMR techniques enabled us to identify the isomeric nature of these adducts. The hydride addition results indicated that the etheric substituent had the predominant effect over the methyl group, leading to a higher addition ratio to the meta-, followed by the ortho-, then the para-positions. It was also clear that in the di-iron system, the hydride addition to each complexed arene ring took place independently. The addition of the cyanide anion to di- and poly-iron arene systems was more selective than that of the hydride anion. Reaction of sodium cyanide with p-methyl- or o-methyl-substituted arene complexes led to the formation of one adduct, with the cyanide being added to the meta position to the etheric bridges. However, cyanide addition to the di-iron complex, with a methyl substituent attached at the meta position of each complexed arene, led to the formation of a mixture of adducts. Cyanide addition to the poly-iron system with p-substituted arenes proved to be very selective, allowing for the formation of one adduct. Oxidative demetallation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) produced the uncomplexed polyaromatic ethers with cyano groups in a very good yield. Key words: cyclopentadienyliron, arene, nucleophilic addition, hydride, cyanide.

Cytokinin Activity of a Group of Ureidopurine Derivatives Related to the tRNA Component, N-(Purin-6-ylcarbamoyl)threonine

1972 ◽  
Vol 50 (3) ◽  
pp. 237-243 ◽  
Author(s):  
W. H. Dyson ◽  
R. H. Hall ◽  
C. I. Hong ◽  
S. P. Dutta ◽  
G. B. Chheda
Keyword(s):  
Side Chain ◽  
Cytokinin Activity ◽  
Molecular Models ◽  
Straight Chain ◽  
Oh Groups ◽  
Alkyl Chains ◽  
Meta Position ◽  
Naturally Occurring ◽  
Intact Organism ◽  
Electronegative Group

Several ureidopurine derivatives have been tested for cytokinin activity in a soya bean callus assay system. N-(Purin-6-ylcarbamoyl)threonine (Ade-CO-Thr), a naturally occurring component of tRNA, is inactive in the assay. Analogues of Ade-CO-Thr having unmodified hydrocarbon side chains are active; optimal activity is associated with tert-butylureidopurine. In the homologous straight chain series n-butylureidopurine is the most active. Introduction of −COOH and/or −OH groups to analogues with otherwise active alkyl chains negates activity.The phenylureidopurine (PUP) derivative is barely active itself, though ortho-halogenated derivatives (o-chloro-, o-fluoro-PUP) are the most potent ureidopurines known. Biological activity decreases rapidly as the electronegative halide is moved from the ortho to the meta position, and lost entirely in the para position. Replacement of the ortho halide with a non-electronegative group (methyl) greatly reduces activity. Molecular models reveal that Ade-CO-Thr and o-chloro-PUP have nearly identical side-chain bulk. The carboxyl groups of Ade-CO-Thr and the chlorine atom of o-chloro-PUP occupy the same position relative to the electronegative carboxyl oxygen of the urea bridge. It is proposed that Ade-CO-Thr has a growth regulatory role in the intact organism, but that exogenous Ade-CO-Thr may be unable to reach the active site.

scholarly journals Impact of Van der Waals interactions on structural and nonlinear optical properties of azobenzene switches

2021 ◽  
Author(s):  
carmelo Naim ◽  
Frédéric Castet ◽  
Eduard Matito
Keyword(s):  
Density Functional ◽  
Nonlinear Optical ◽  
Van Der Waals Interactions ◽  
Dispersion Interactions ◽  
Geometrical Structures ◽  
Hartree Fock ◽  
Meta Position ◽  
Good Account ◽  
London Dispersion ◽  
Azobenzene Derivatives

<div> <div> <div> <p>The geometrical structures, relative Z-E energies, and second-order nonlinear responses of a collection of azobenzene molecules symmetrically substituted in meta- position with functional groups of different bulkiness are investigated using various ab initio and DFT levels of approximation. We show that RI-MP2 and RI-CC2 approximations provide very similar geometries and relative energies and evidence that London dispersion interactions existing between bulky meta-substituents stabilize the Z con- former. The !B97-X-D exchange-correlation functional provides an accurate description of these effects and gives a good account of the nonlinear optical response of the molecules. We show that density functional approximations should include no less than 50% of Hartree-Fock exchange to provide accurate hyperpolarizabilities. A property-structure analysis of the azobenzene derivatives reveals that the main contribution to the first hyperpolarizability comes from the azo bond, but phenyl meso-substituents can enhance it.</p> </div> </div> </div>

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