scholarly journals Conservation of direct dynamics in sterically hindered SN2/E2 reactions

2018 ◽  
Vol 9 (3) ◽  
pp. 693-701 ◽  
Author(s):  
Eduardo Carrascosa ◽  
Jennifer Meyer ◽  
Tim Michaelsen ◽  
Martin Stei ◽  
Roland Wester
Keyword(s):  
Nucleophilic Substitution ◽  
Steric Hindrance ◽  
Velocity Map Imaging ◽  
Direct Dynamics ◽  
Beam Velocity ◽  
Sterically Hindered

The effect of steric hindrance on the stereodynamics of nucleophilic substitution (SN2) and base-induced elimination (E2) has been studied using crossed-beam velocity map imaging.

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>

Nucleophilic Substitution Reactions of Tetrabutylammonium aci-Nitronates with p-Substituted Nitrobenzenes

1979 ◽  
Vol 32 (11) ◽  
pp. 2413 ◽  
Author(s):  
RK Norris ◽  
D Randles
Keyword(s):  
Dimethyl Sulfoxide ◽  
Nucleophilic Substitution ◽  
Lithium Salts ◽  
Methyl Groups ◽  
The Novel ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Sterically Hindered

The reactions of tetrabutylammonium aci-nitronates with p-dinitrobenzene in dimethyl sulfoxide, benzene or acetone proceed far more rapidly than the reactions of the corresponding lithium salts and give, in unhindered cases, good yields of C-arylates, e.g. p-(1-methyl-1-nitroethyl)nitrobenzene (in 73-89% yields) and p-nitro(l,3,3-trimethyl-1-nitrobuty1)benene (in 70% yield). With more sterically hindered nitronates, O-arylation increases, giving phenols and ketoxime O-p-nitrophenyl ethers, presumably derived from the novel, intermediate p-nitrophenyl aci-nitronate esters. aci-Nitronate ions with more than two β-methyl groups gave no C-arylation. Similar results were obtained with p-fluoronitrobenzene and p-nitrobenzonitrile, A mechanism for the conversion of the intermediate aci-nitronate esters into the ketoxime ethers is proposed.

The effect of steric hindrance on the SRN1 reaction of some α-Alkyl-p-nitrobenzyl chlorides

1976 ◽  
Vol 29 (12) ◽  
pp. 2621 ◽  
Author(s):  
RK Norris ◽  
D Randles
Keyword(s):  
Oxygen Atom ◽  
Steric Hindrance ◽  
Lithium Salt ◽  
Dimethyl Sulphoxide ◽  
Sterically Hindered ◽  
Srn1 Reaction

The reactions of a series of α-substituted p-nitrobenzyl chlorides, p- NO2C6H4CH(Cl)R (R = Me, Et, Prt, But), with the lithium salt of 2- nitropropane in dimethyl sulphoxide and dimethylformamide have been studied. When R = Me or Et, competing SRN1 and SN2 processes take place, giving C- and O-alkylated products respectively. In the more sterically hindered cases where R = Pri or But, the only reaction taking place has been shown to be an SRN1 reaction with exclusive O-alkylation. These observations indicate that the SRN1 reaction is prone to steric hindrance, and that radical alkylation of the ambident nitronate ion occurs on the more accessible oxygen atom in sterically hindered situations.

scholarly journals The role of steric hindrance in the intramolecular oxidative aromatic coupling of pyrrolo[3,2-b]pyrroles

2016 ◽  
Vol 52 (77) ◽  
pp. 11539-11542 ◽  
Author(s):  
Maciej Krzeszewski ◽  
Paweł Świder ◽  
Łukasz Dobrzycki ◽  
Michał K. Cyrański ◽  
Witold Danikiewicz ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Steric Hindrance ◽  
Sterically Hindered

Sterically hindered tetraaryl-pyrrolo[3,2-b]pyrroles undergo oxidative aromatic coupling, forming a fluorene scaffold linked via a spiro carbon atom with a novel π-conjugated scaffold.

High- and low-spin complexes with similar, ligands. II. Iron(II) complexes with sterically hindered analogues of 2,2'-bipyridyl

1972 ◽  
Vol 25 (8) ◽  
pp. 1631 ◽  
Author(s):  
CM Harris ◽  
S Kokot ◽  
HRH Patil ◽  
E Sinn ◽  
H Wong
Keyword(s):  
Spectral Data ◽  
High Spin ◽  
Steric Hindrance ◽  
Field Potential ◽  
Ligand Field ◽  
Apparent Difference ◽  
Field Splitting ◽  
Analogous Complex ◽  
Sterically Hindered ◽  
Direct Change

Benzo substitution cis to the nitrogen of 2,2'-bipyridyl (bipy), to form 2-(2'-pyridyl)quinoline (pq), transforms the tris-complex with iron(11) from low spin in Fe(bipy)32+ to essentially high spin but near the crossover in Fe(pq)32+. For this complex, the ligand field splitting near the crossover, Δc is estimated from magnetic and spectral data as c. 12000 cm-l. A similar value but 150 cm-l lower is estimated for the analogous complex with the sterically related ligand 2-methyl-1,10-phenanthroline. This apparent difference in Δ values could arise from a direct change in ligand field potential, or from other factors, such as a change in distortion effects. Due to steric hindrance, pq prefers to form bis-complexes Fe(pq)2X2, pseudooctahedral and high spin, with suitable monodentates, X = Cl2 Br, NCS, ClO4. Double benzo substitution of bipy to form 2,2'-biquinolyl (biq) so increases steric hindrance that the tris-complex could not be formed. Instead biq forms pseudotetrahedral complexes Fe(biq)22+ and Fe(biq)X2 (X = Cl, Br).

Heats of mixing of trialkylamines: disorder and steric hindrance contributions

1978 ◽  
Vol 56 (22) ◽  
pp. 2856-2865 ◽  
Author(s):  
Robert Philippe ◽  
Geneviève Delmas ◽  
Phuong Nguyen Hong
Keyword(s):  
Steric Hindrance ◽  
Significant Contribution ◽  
Orientational Order ◽  
Class A ◽  
Heats Of Mixing ◽  
Class B ◽  
Chain Compounds ◽  
Sterically Hindered ◽  
Long Chain ◽  
Long Chains

Nine trialkylamines, triethyl- to trihexylamine trioctyl-, tridodecyl, tri(methyl-2-butyl)-, and dimethyldodecylamine have been used for heats of mixing of the following systems at 298 K: A, fourteen systems made of all the possible binary mixtures (except one) of the six shorter amines; B, twelve systems made of a long chain amine, trioctyl-, tridodecyl- or dimethyldodecylamine with the four shorter members of the series; C, two systems consisting of the mixture of two long-chain compounds, trioctylamine with tridodecyl- and dimethyldodecylamine. Heats for the class A systems are less than or equal to 40 J/mol, indicating no net effect of the small polarity of the shorter members of the series. The experimental HE of these mixtures are compared with two theories. The Monte Carlo approach gives good predictions but the heats calculated with the Snider–Herrington theory are too negative. Heats of the class B systems are suitable for the investigation of two new contributions to the heats of mixing, the positive heat of disordering of long-chains HE(dis.) and the negative heat found in systems where one of the components is sterically hindered, HE(ster.hindr.). HE(dis.) found with the long-chain amines indicates an orientational order larger than in the case of the n-alkane of the same chain-length but equivalent to that found in the tetraalkyltin compounds of the same length. Recent work has shown that the tetrapropyl and tetraethyltin derivatives when mixed with long-chain alkanes or tin derivatives give rise to a HE(ster.hindr.) contribution. From this work and the present study, the steric hindrance contributions of five sterically hindered compounds tetraethyltin and tetrapropyltin, triethyl- and tripropylamine, and 3,3-diethylpentane mixed with different second components are calculated. The steric hindrance contribution is found proportional to the volume of the second component and increasing in the following order of the sterically hindered component: triethyl- < tripropylamine < tetraethyl- < tetrapropyltin < 3,3-diethylpentane. Heats of the class C systems are small without significant contribution of HE(dis.) due to the fitting of the long-chains in solution.

N,N-Dialkyl-N′-Chlorosulfonyl Chloroformamidines in Heterocyclic Synthesis. Part XV. Some Unexpected Reactions with Anilines

2018 ◽  
Vol 71 (8) ◽  
pp. 610
Author(s):  
Dylan Innes ◽  
Michael V. Perkins ◽  
Andris J. Liepa ◽  
Craig L. Francis
Keyword(s):  
Nucleophilic Substitution ◽  
Membered Ring ◽  
Heterocyclic Synthesis ◽  
Screening Programs ◽  
Bioactive Molecule ◽  
Sterically Hindered

N,N-Dimethyl-N′-chlorosulfonyl chloroformamidine 1a underwent reactions with various anilines. In addition to the benzo[e][1,2,4]thiadiazine dioxides 8, from 1,3-NCC bis-nucleophilic substitution and bis-anilino adducts 9, some unexpected products were formed, particularly when sterically hindered or electron-poor anilines were used. In these cases, products such as the [1,3,2,4,6]dithiatriazine 1,1,3,3-tetraoxides 17 and, on occasion, N,N,5-trimethyl-4-(arylimino)-4,5-dihydro-[1,3,5]triazin-2-amines 14 were produced in significant yields. Reaction of dichloride 1a with 3-bromoaniline afforded the unusual eight-membered-ring product 2,6-bis(3-bromophenyl)-3,7-bis(dimethylamino)-2H,6H-[1,5,2,4,6,8]dithiatetrazocine 1,1,5,5-tetraoxide 28, in addition to the dithiatriazine tetraoxide 17k. These uncommon heterocyclic structures are of interest for bioactive molecule discovery screening programs.

scholarly journals Insight into the antitumor actions of sterically hindered platinum(ii) complexes by a combination of STD NMR and LCMS techniques

Metallomics ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 427-434
Author(s):  
Zhimei Wang ◽  
Lei Fang ◽  
Jian Zhao ◽  
Shaohua Gou
Keyword(s):  
Drug Delivery ◽  
Steric Hindrance ◽  
Std Nmr ◽  
Sterically Hindered ◽  
Insight Into

The introduction of suitable steric hindrance groups to platinum(ii) complexes is beneficial for drug delivery and overcoming the drawbacks of the current platinum(ii) complexes.

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