ChemInform Abstract: THERMAL DECARBOXYLATION OF β-LACTONES: STERIC HINDRANCE OF MESOMERISM AS A HINT TO A ZWITTERIONIC INTERMEDIATE STAGE

1980 ◽  
Vol 11 (40) ◽  
Author(s):  
J. MULZER ◽  
M. ZIPPEL ◽  
G. BRUENTRUP
Keyword(s):  
Steric Hindrance ◽  
Intermediate Stage ◽  
Zwitterionic Intermediate ◽  
Thermal Decarboxylation

Réactions de substitution homolytique. V. Stéréosélectivité de différents radicaux cyclohexyles

1976 ◽  
Vol 54 (6) ◽  
pp. 905-909 ◽  
Author(s):  
Michel Gruselle ◽  
Jacques Fossey ◽  
Daniel Lefort ◽  
Claude Lamarre ◽  
Jean-Claude Richer
Keyword(s):  
Steric Hindrance ◽  
Substitution Reaction ◽  
Steric Effects ◽  
Relative Importance ◽  
Peroxy Acid ◽  
Radical Site ◽  
Peroxy Acids ◽  
Homolytic Substitution ◽  
Thermal Decarboxylation ◽  
As If

The influence of the environment near the radical site on the stereoselectivity of the homolytic substitution reaction of variously substituted cyclohexyl radicals on the peroxidic oxygen of a peroxy acid has been studied using the thermal decarboxylation of peroxy acids. This reaction leads to stereoisomeric alcohols[Formula: see text]The radical behaves as if it were planar and, in general, an axial approach of the reagent is strongly favoured except when substituents increase the steric hindrance of the radical.The stereoselectivity is explained in terms of the relative importance of steric effects (for the axial approach) and of bond interactions (for the equatorial approach). It also depends on the flexibility of the ring. [Journal translation]

Solar Filaments as Tracers of Subsurface Processes

2000 ◽  
Vol 179 ◽  
pp. 177-183
Author(s):  
D. M. Rust
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Coronal Mass Ejections ◽  
Interplanetary Space ◽  
Intermediate Stage ◽  
Coronal Plasma ◽  
Magnetic Helicity ◽  
The Sun ◽  
New Paradigm ◽  
Solar Filaments

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.

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

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>

The results of the study of the workers’ health according to the survey

2020 ◽  
pp. 793-793
Author(s):  
M. A. Fesenko ◽  
E. V. Zueva ◽  
E. V. Fedorova
Keyword(s):  
Medical Research ◽  
Working Conditions ◽  
Intermediate Stage ◽  
The State

The possibility of using the survey as an intermediate stage of assessing the state of working conditions and health of workers. It is concluded that this method is not applicable as an independent device but can be used with other methods of medical research.

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