Conformational effects on the 2,3-sigmatropic shift of sulfur-stabilized ylides and enolates involving bicyclic transition states

1979 ◽  
Vol 44 (18) ◽  
pp. 3230-3238 ◽  
Author(s):  
Edwin Vedejs ◽  
Michael J. Arnost ◽  
James P. Hagen
Keyword(s):  
Transition States ◽  
Conformational Effects ◽  
Sigmatropic Shift

Transition state geometry in the scission and formation of cyclopentane and cyclohexane oxiranes. Use of the dilatometer in studying mixed reactions of different orders

1979 ◽  
Vol 57 (18) ◽  
pp. 2444-2457 ◽  
Author(s):  
John W. Bovenkamp ◽  
Edward J. Langstaff ◽  
Robert Y. Moir ◽  
Robert A. B. Bannard
Keyword(s):  
Inductive Effect ◽  
Transition States ◽  
Accurate Method ◽  
High Specific Surface Area ◽  
Ion Pair ◽  
Third Order ◽  
Dipole Interactions ◽  
Conformational Effects ◽  
Cyclopentane Ring ◽  
Transition State Geometry

Two methods, one more accurate, the other more convenient, were developed by which the dilatometer could be used with concurrent reactions of the second and third order. The more accurate method, employing a dilatometer of high specific surface area and equipped with a stable and responsive thermometer, was used in studying as many as six simultaneous oxirane scissions in acid solution. Interlocking double comparisons were made between cyclohexane and cyclopentane ring systems, between systems possessing or lacking a methoxyl substituent and between others having the substituent in varying orientations, between charged and uncharged nucleophiles, and between transition states of different degrees of protonation. Searching experimental checks were therefore possible in four main areas: (i) a quantitative dissection of the inductive effect from steric and conformational effects, and from dipole–ion or dipole–dipole interactions with the nucleophile, (ii) a quantitative demonstration of three main differences between transition states based on 5- and 6-membered rings, (iii) a proof that syn-1,3-effects in the transition states are very charge dependent, being large and positive with unfavourably arranged dipoles, and small or perhaps negative with favourable arrangements, and (iv) a rejection of certain proposed ion-pair alternatives to the A2 mechanism.

Theoretical Computations on the Pyrolysis of Alkyl (dithio)acetates

2020 ◽  
Vol 17 (3) ◽  
pp. 224-233
Author(s):  
Xun Zhu ◽  
Chen Jian ◽  
Xiuqin Zhou ◽  
Abdullah M. Asiri ◽  
Khalid A. Alamry ◽  
...  
Keyword(s):  
Transition States ◽  
Membered Ring ◽  
Pyrolysis Process ◽  
Alkyl Esters ◽  
Charge Distributions ◽  
Theoretical Analyses

The pyrolysis of methyl alkyl esters I to III and dithioesters IV to VI were theoretically calculated. All possible pyrolysis paths were considered. Both esters and dithioesters presented three potential paths via six-, four- and five-membered ring transition states, respectively. The calculation processes were calculated using MP2/6-31G(d) set. In-depth theoretical analyses were also presented, including NBO related analyses, synchronicities, and charge distributions, to reveal the detailed pyrolysis process.

Sterically Crowded Heterocycles. X. A New Mechanistic Approach to the Ferricyanide Oxidation of 4,6'-Disubstituted 1-(Pyridin-2'-yl)-2,6-diphenylpyridinium Salts

1999 ◽  
Vol 64 (8) ◽  
pp. 1274-1294 ◽  
Author(s):  
Radek Pohl ◽  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Transition States ◽  
Oxidative Transformation ◽  
Steric Interactions ◽  
Radical Intermediates ◽  
Mechanistic Approach

The oxidations of the title perchlorates, bearing the sterically diverse 6'-substituents (H, Me, Et, i-Pr, n-Bu, t-Bu and Ph) in two series with the same 4-substituents (Ph and t-Bu) lead to pairs of isomeric 3',5-disubstituted (Z)-1'-phenyl-3'-(2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2'- en-1'-ones and 3,6'-disubstituted [5-phenyl-1-(6'-pyridin-2'-yl)-1H-pyrrol-2-yl](phenyl)methanones except where the both variable substituents are t-Bu and then only pyrrolic product is formed. Considering steric interactions of the substituents in some intermediate and/or transition states a multistep mechanism for the oxidative transformation is proposed and supported by model PM3-PECI calculations of some radical intermediates.

scholarly journals Quantitative Analysis of the Membrane Affinity of Local Anesthetics Using a Model Cell Membrane

Membranes ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 579
Author(s):  
Wanjae Choi ◽  
Hyunil Ryu ◽  
Ahmed Fuwad ◽  
Seulmini Goh ◽  
Chaoge Zhou ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Local Anesthetics ◽  
Electrophysiological Study ◽  
Local Area ◽  
Membrane Properties ◽  
Dominant Factor ◽  
Free Standing ◽  
Membrane Affinity ◽  
Conformational Effects ◽  
Model Protein

Local anesthesia is a drug that penetrates the nerve cell membrane and binds to the voltage gate sodium channel, inhibiting the membrane potential and neurotransmission. It is mainly used in clinical uses to address the pain of surgical procedures in the local area. Local anesthetics (LAs), however, can be incorporated into the membrane, reducing the thermal stability of the membrane as well as altering membrane properties such as fluidity, permeability, and lipid packing order. The effects of LAs on the membrane are not yet fully understood, despite a number of previous studies. In particular, it is necessary to analyze which is the more dominant factor, the membrane affinity or the structural perturbation of the membrane. To analyze the effects of LAs on the cell membrane and compare the results with those from model membranes, morphological analysis and 50% inhibitory concentration (IC50) measurement of CCD-1064sk (fibroblast, human skin) membranes were carried out for lidocaine (LDC) and tetracaine (TTC), the most popular LAs in clinical use. Furthermore, the membrane affinity of the LAs was quantitatively analyzed using a colorimetric polydiacetylene assay, where the color shift represents their distribution in the membrane. Further, to confirm the membrane affinity and structural effects of the membranes, we performed an electrophysiological study using a model protein (gramicidin A, gA) and measured the channel lifetime of the model protein on the free-standing lipid bilayer according to the concentration of each LA. Our results show that when LAs interact with cell membranes, membrane affinity is a more dominant factor than steric or conformational effects of the membrane.

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