An air-persistent oxyallyl radical cation with simple di(methyl)amino substituents

2016 ◽  
Vol 52 (76) ◽  
pp. 11422-11425 ◽  
Author(s):  
Vianney Regnier ◽  
Florian Molton ◽  
Christian Philouze ◽  
David Martin
Keyword(s):  
Radical Cation ◽  
Steric Hindrance

Despite minimal steric hindrance, the 1,1,3,3-tetrakis(dimethylamino) oxyallyl radical cation is persistent for several hours in well-aerated solutions.

scholarly journals Exceptionally Long Covalent CC Bonds—A Local Vibrational Mode Study

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 950
Author(s):  
Alexis Antoinette Ann Delgado ◽  
Alan Humason ◽  
Robert Kalescky ◽  
Marek Freindorf ◽  
Elfi Kraka
Keyword(s):  
Bond Strength ◽  
Radical Cation ◽  
Steric Hindrance ◽  
Force Constants ◽  
Electronic Effects ◽  
Future Design ◽  
Local Vibrational Mode ◽  
Negative Hyperconjugation ◽  
New Guidelines ◽  
First Time

For decades one has strived to synthesize a compound with the longest covalent C−C bond applying predominantly steric hindrance and/or strain to achieve this goal. On the other hand electronic effects have been added to the repertoire, such as realized in the electron deficient ethane radical cation in its D3d form. Recently, negative hyperconjugation effects occurring in diamino-o-carborane analogs such as di-N,N-dimethylamino-o-carborane have been held responsible for their long C−C bonds. In this work we systematically analyzed CC bonding in a diverse set of 53 molecules including clamped bonds, highly sterically strained complexes such as diamondoid dimers, electron deficient species, and di-N,N-dimethylamino-o-carborane to cover the whole spectrum of possibilities for elongating a covalent C−C bond to the limit. As a quantitative intrinsic bond strength measure, we utilized local vibrational CC stretching force constants ka(CC) and related bond strength orders BSO n(CC), computed at the ωB97X-D/aug-cc-pVTZ level of theory. Our systematic study quantifies for the first time that whereas steric hindrance and/or strain definitely elongate a C−C bond, electronic effects can lead to even longer and weaker C−C bonds. Within our set of molecules the electron deficient ethane radical cation, in D3d symmetry, acquires the longest C−C bond with a length of 1.935 Å followed by di-N,N-dimethylamino-o-carborane with a bond length of 1.930 Å. However, the C−C bond in di-N,N-dimethylamino-o-carborane is the weakest with a BSO n value of 0.209 compared to 0.286 for the ethane radical cation; another example that the longer bond is not always the weaker bond. Based on our findings we provide new guidelines for the general characterization of CC bonds based on local vibrational CC stretching force constants and for future design of compounds with long C−C bonds.

Para-Selective Borylation of Monosubstituted Arenes Using a Transient Mediator

2019 ◽  
Author(s):  
Jie Wu ◽  
Xiao-Yue Chen ◽  
Yichen Wu ◽  
Daoming Wang ◽  
Peng Wang
Keyword(s):  
Radical Cation ◽  
Steric Hindrance ◽  
Mechanistic Study ◽  
Salt Formation ◽  
Sulfonium Salt ◽  
Trifluoromethanesulfonic Anhydride ◽  
In Situ Generation

Herein, we conceptualized a transient mediator approach that has the capability of <i>para</i>-selective C–H functionalization of monosubstituted aromatics. This approach is enabled by in situ generation of a versatile sulfonium salt via highly electrophilic phenoxathiine or thianthrene radical cation intermediate which can be readily generated from its sulfoxide with trifluoromethanesulfonic anhydride. Preliminary mechanistic study unveiled that the remarkable <i>para</i> selectivity is related to the incredible electrophilicity and steric hindrance of phenoxathiine or thianthrene radical cation. The versatility of this approach was demonstrated via <i>para</i>-borylation of various monosubstituted simple aromatics combining the sulfonium salt formation with further photocatalyzed transformation.

Para-Selective Borylation of Monosubstituted Arenes Using a Transient Mediator

2019 ◽  
Author(s):  
Jie Wu ◽  
Xiao-Yue Chen ◽  
Yichen Wu ◽  
Daoming Wang ◽  
Peng Wang
Keyword(s):  
Radical Cation ◽  
Steric Hindrance ◽  
Mechanistic Study ◽  
Salt Formation ◽  
Sulfonium Salt ◽  
Trifluoromethanesulfonic Anhydride ◽  
In Situ Generation

Herein, we conceptualized a transient mediator approach that has the capability of <i>para</i>-selective C–H functionalization of monosubstituted aromatics. This approach is enabled by in situ generation of a versatile sulfonium salt via highly electrophilic phenoxathiine or thianthrene radical cation intermediate which can be readily generated from its sulfoxide with trifluoromethanesulfonic anhydride. Preliminary mechanistic study unveiled that the remarkable <i>para</i> selectivity is related to the incredible electrophilicity and steric hindrance of phenoxathiine or thianthrene radical cation. The versatility of this approach was demonstrated via <i>para</i>-borylation of various monosubstituted simple aromatics combining the sulfonium salt formation with further photocatalyzed transformation.

Steric hindrance influence of a diazo link upon mesogenic properties of some ligands and related copper complexes

1997 ◽  
Vol 94 ◽  
pp. 1695-1714 ◽  
Author(s):  
P Lesot ◽  
F Perez ◽  
P Judeinstein ◽  
JP Bayle ◽  
H Allouchi ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Copper Complexes

The electronic properties of a radical cation salt of bis-ethylenedioxodibenzofuran, [(bEDODBF)5 (AsF6)2(CH2Cl 2)0.2]

1988 ◽  
Vol 49 (4) ◽  
pp. 667-673 ◽  
Author(s):  
S. Söderholm ◽  
J. Hellberg ◽  
G. Ahlgren ◽  
M. Krebs ◽  
J.U. von Schütz ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Radical Cation ◽  
Radical Cation Salt

METABOLISM OF 17α-HYDROXYPROGESTERONE-4-14C-17α-CAPROATE BY HOMOGENATES OF RAT LIVER AND HUMAN PLACENTA

1961 ◽  
Vol 36 (4) ◽  
pp. 511-519 ◽  
Author(s):  
Margaret Wiener ◽  
Charles I. Lupa ◽  
E. Jürgen Plotz
Keyword(s):  
Rat Liver ◽  
Human Placenta ◽  
Steric Hindrance ◽  
Placental Tissue ◽  
Caproic Acid ◽  
Major Product ◽  
Side Chain ◽  
Anaerobic Conditions ◽  
Prolonged Action ◽  
Long Acting

ABSTRACT 17α-hydroxyprogesterone-4-14C-17α-caproate (HPC), a long-acting progestational agent, was incubated with homogenates of rat liver and human placenta. The rat liver was found to reduce Ring A of HPC under anaerobic conditions to form allopregnane-3β,17α-diol-20-one-17α-caproate and pregnane-3β,17α-diol-20-one-17α-caproate, the allopregnane isomer being the major product. The caproic acid ester was neither removed nor altered during the incubation. Placental tissue did not attack HPC under conditions where the 20-ketone of progesterone was reduced. It is postulated that this absence of attack on the side chain is due to steric hindrance from the caproate ester, and that this may account for the prolonged action of HPC.

Tyrosine-Selective Bioconjugation with Iminoxyl Radicals

2020 ◽  
Author(s):  
Katsuya Maruyama ◽  
Takashi Ishiyama ◽  
Yohei Seki ◽  
Kounosuke Oisaki ◽  
Motomu Kanai
Keyword(s):  
Reaction Time ◽  
Steric Hindrance ◽  
Room Temperature ◽  
Water Soluble ◽  
Light Irradiation ◽  
Sodium Ascorbate ◽  
Iminoxyl Radical ◽  
Short Reaction Time ◽  
Modified Peptides ◽  
The Stability

A novel Tyr-selective protein bioconjugation using the water-soluble persistent iminoxyl radical is described. The conjugation proceeded with high Tyr-selectivity and short reaction time under biocompatible conditions (room temperature in buffered media under air). The stability of the conjugates was tunable depending on the steric hindrance of iminoxyl. The presence of sodium ascorbate and/or light irradiation promoted traceless deconjugation, restoring the native Tyr structure. The method is applied to the synthesis of a protein-dye conjugate and further derivatization to azobenzene-modified peptides.

Synthesis of Conjugated Triynes via Alkyne Metathesis

2019 ◽  
Author(s):  
Idriss Curbet ◽  
Sophie Colombel-Rouen ◽  
Romane Manguin ◽  
Anthony Clermont ◽  
Alexandre Quelhas ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
High Selectivity ◽  
Alkyne Metathesis ◽  
Cross Metathesis ◽  
Synthetic Strategy ◽  
Sterically Hindered ◽  
Site Selective

<div> <div> <div> <div> <p>The synthesis of conjugated triynes by molybdenum-catalyzed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site- selective alkyne metathesis to produce the desired con- jugated triyne products. The steric hindrance of alkyne moiety was found to be crucial in preventing the for- mation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity. </p> </div> </div> </div> </div>

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