Electrophilic additions to allenes. VI. The role of steric versus electronic effects in the reactions of arenesulphenyl halides with allenes

1980 ◽  
Vol 58 (24) ◽  
pp. 2737-2744 ◽  
Author(s):  
Dennis G. Garrattz ◽  
Pierre L. Beaulieu
Keyword(s):  
Positive Charge ◽  
Steric Effects ◽  
Rate Data ◽  
Electronic Effects ◽  
Rate Determining Step ◽  
Minimal Importance ◽  
Electrophilic Additions

The role of steric and electronic effects during the rate and product determining steps for the addition of arenesulphenyl chlorides to 1,3-disubstituted allenes has been briefly examined. Both effects appear to be generally of minimal importance during the rate determining step. The available rate data indicate the presence of little, if any, build up of positive charge on sulphur. These results are interpreted in terms of an SN2 attack on bivalent sulphur leading to an alkylidenethiiranium ion intermediate. Steric effects are of greater importance in the product determining step, particularly when the sulphenyl chlorides possess two bulky ortho substituents, as in the case of 2,4,6-triisopropylbenzenesulphenyl chloride.

A DFT/MM analysis of the effect of ligand substituents on asymmetric hydrogenation catalyzed by rhodium complexes with phosphine–phosphinite ligands

2009 ◽  
Vol 87 (10) ◽  
pp. 1273-1279 ◽  
Author(s):  
Steven M. A. Donald ◽  
Anton Vidal-Ferran ◽  
Feliu Maseras
Keyword(s):  
Dft Calculations ◽  
Asymmetric Hydrogenation ◽  
Rhodium Catalyst ◽  
Experimental Results ◽  
Catalytic Process ◽  
Rhodium Complexes ◽  
Electronic Effects ◽  
Rate Determining Step ◽  
Bidentate Phosphine

DFT and DFT/MM calculations are carried out on the rate-determining step of the addition of dihydrogen to methyl-(N)-acetylaminoacrylate catalyzed by a rhodium catalyst containing a bidentate phosphine–phosphinite ligand. DFT calculations reproduce the experimental results, while DFT/MM calculations do not. The failure of DFT/MM methods for this particular problem is analyzed through a series of calculations with different partitions between the DFT and MM regions, which show that electronic effects of all ligand substituents considered are critical. The analysis of these electronic effects provides key information on the role of each of the substituents in the outcome of the overall catalytic process.

Electrophilic additions to allenes. VII. The role of steric versus electronic effects in the reactions of areneselenenyl halides with allenes

1980 ◽  
Vol 58 (24) ◽  
pp. 2745-2753 ◽  
Author(s):  
Dennis G. Garratt ◽  
Pierre L. Beaulieu ◽  
Veronique M. Morisset ◽  
Mark Ujjainwalla
Keyword(s):  
Methylene Chloride ◽  
Transition States ◽  
Similar Rate ◽  
Steric Interaction ◽  
Electronic Effects ◽  
Methylene Chloride Solution ◽  
Product Distributions ◽  
Electrophilic Additions ◽  
Rate Limiting

The reactions of benzeneselenenyl chloride, bromide, and 2,4,6-trimethylbenzeneselenenyl bromide with alkyl 1,3-disubstituted allenes in methylene chloride solution have been investigated. While kinetic data are in accord with similar rate determining transition states, exhibiting strong steric effects for ail three species, the product distributions show changes in both chemoselectivity and configurational-selectivity in accord with two different types of steric interaction mechanisms during the product determining transition states. A mechanism involving rate limiting formation of alkylideneseleniranium ions and/or alkylideneepiselenuranes, followed by isomerization between the alkylideneseleniranium ions by a path not involving allylic ions, prior to the product determining transition states, is proposed.

A β-cyclodextrin–resveratrol inclusion complex and the role of geometrical and electronic effects on its electronic induced circular dichroism

RSC Advances ◽  
2013 ◽  
Vol 3 (26) ◽  
pp. 10242 ◽  
Author(s):  
Eduardo Troche-Pesqueira ◽  
Ignacio Pérez-Juste ◽  
Armando Navarro-Vázquez ◽  
María Magdalena Cid
Keyword(s):  
Circular Dichroism ◽  
Inclusion Complex ◽  
Induced Circular Dichroism ◽  
Electronic Effects ◽  
Circular Dichroïsm

scholarly journals Evaluation of Electronic Effects in the Solvolyses ofp-Methylphenyl andp-Chlorophenyl Chlorothionoformate Esters

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Malcolm J. D’Souza ◽  
Olivia N. Hampton ◽  
Brett M. Sansbury ◽  
Dennis N. Kevill
Keyword(s):  
Rate Data ◽  
Electronic Effects ◽  
Titration Method ◽  
Organic Mixtures

The solvolyses ofp-tolyl chlorothionoformate andp-chlorophenyl chlorothionoformate are studied in a variety of organic mixtures of widely varying nucleophilicity and ionizing power values. This solvolytic data is accumulated at 25.0°C using the titration method. An analysis of the rate data using the extended (two-term) Grunwald-Winstein equation and the concept of similarity of substrates based on theirl/mratios shows the occurrence of simultaneous side-by-side addition-elimination and unimolecularSN1 mechanisms.

Steric Effects in the Electronic Spectra of the 3,5-Diarylaminobenzene Derivatives

1986 ◽  
Vol 41 (11) ◽  
pp. 1311-1314 ◽  
Author(s):  
A. Balter ◽  
W. Nowak ◽  
P. Milart ◽  
J. Sepioł
Keyword(s):  
Excited State ◽  
Electronic Spectra ◽  
Fluorescence Properties ◽  
Steric Effects ◽  
Quantum Yields ◽  
Spectroscopic Behaviour ◽  
Fluorescence Quantum Yields ◽  
Excited State Lifetimes ◽  
Methyl Phenyl

Absorption and fluorescence properties, excited state lifetimes and fluorescence quantum yields were determined for a series of 3,5-diarylaminobenzene derivatives in solvents of different polarities. The role of the nitrile, methyl, phenyl and naphthyl substituents is discussed. Especially the steric effects on the spectroscopic behaviour of the investigated molecules are studied.

scholarly journals Propranolol Inhibits Hyphal Development in Candida albicans

2002 ◽  
Vol 46 (11) ◽  
pp. 3617-3620 ◽  
Author(s):  
Carol A. Baker ◽  
Kevin Desrosiers ◽  
Joseph W. Dolan
Keyword(s):  
Growth Rate ◽  
Candida Albicans ◽  
Phosphatidic Acid ◽  
Rate Data ◽  
Dimorphic Transition ◽  
Hyphal Development ◽  
Germ Tubes ◽  
Hydrolysis Of

ABSTRACT Propranolol was used to investigate the role of phosphatidic acid (PA) and diacylglycerol in the dimorphic transition in Candida albicans. Propranolol was able to inhibit the appearance of germ tubes without decreasing growth rate. Data suggest that inhibition of morphogenesis may be due to binding by propranolol of PA derived from PLD1 hydrolysis of phosphatidylcholine.

Role of S4 positively charged residues in the regulation of Kv4.3 inactivation and recovery

2007 ◽  
Vol 293 (3) ◽  
pp. C906-C914 ◽  
Author(s):  
Matthew R. Skerritt ◽  
Donald L. Campbell
Keyword(s):  
Positive Charge ◽  
Voltage Sensitivity ◽  
Shaker Channels ◽  
Recovery From Inactivation ◽  
Kv4 Channels ◽  
Charged Residues ◽  
Arginine Residues ◽  
Voltage Sensing Domain ◽  
Positively Charged

The molecular and biophysical mechanisms by which voltage-sensitive K+ (Kv)4 channels inactivate and recover from inactivation are presently unresolved. There is a general consensus, however, that Shaker-like N- and P/C-type mechanisms are likely not involved. Kv4 channels also display prominent inactivation from preactivated closed states [closed-state inactivation (CSI)], a process that appears to be absent in Shaker channels. As in Shaker channels, voltage sensitivity in Kv4 channels is thought to be conferred by positively charged residues localized to the fourth transmembrane segment (S4) of the voltage-sensing domain. To investigate the role of S4 positive charge in Kv4.3 gating transitions, we analyzed the effects of charge elimination at each positively charged arginine (R) residue by mutation to the uncharged residue alanine (A). We first demonstrated that R290A, R293A, R296A, and R302A mutants each alter basic activation characteristics consistent with positive charge removal. We then found strong evidence that recovery from inactivation is coupled to deactivation, showed that the precise location of the arginine residues within S4 plays an important role in the degree of development of CSI and recovery from CSI, and demonstrated that the development of CSI can be sequentially uncoupled from activation by R296A, specifically. Taken together, these results extend our current understanding of Kv4.3 gating transitions.

From the Understanding of the Reaction Mechanism Towards Optimizing the Deposition Rate and Optoelectronic Properties of a-Si:H

1989 ◽  
Vol 149 ◽  
Author(s):  
S. Veprek ◽  
M. Heintze ◽  
R. Bayer ◽  
N. Jurčik-Rajman
Keyword(s):  
Reaction Mechanism ◽  
Surface Coverage ◽  
Kinetic Studies ◽  
Reactive Intermediates ◽  
Sticking Coefficient ◽  
High Quality ◽  
Rate Determining Step ◽  
Homogeneous Good ◽  
Good Agreement

ABSTRACTWe present new results of kinetic studies of the deposition of high quality a-Si:H which strongly support the reaction mechanism suggested in our earlier papers: 1. SiH4 → SiH2; 2. SiH2 + SiS4 → Si2H6 (SiH2 + Si2H6 → Si3H6); 3. Si2H6 → 2a-Si:H (Si3H8 → 3a-Si:H). The “SiH3 mechanism”, as promoted by several workers, is in contradiction with these experimental facts.The di- and trisilane, which have a much higher reactive sticking coefficient than monosilane, play the role of reactive intermediates which facilitate the heterogeneous decomposition of silicon carrying species at the surface of the growing film. The values of the reactive sticking coefficient of Si2H6 and Si3H8 depend on the surface coverage by chemisorbed hydrogen; they increase with decreasing surface coverage. Under the conditions of the growth of high quality a-Si:H films the reactive sticking coefficient of disilane amounts to 10−4 to 10−2 which is in a good agreement with recent data of other authors.The rate determining step of the growth of high quality a-Si:H films is the desorption of hydrogen from the surface of the growing film. This can be strongly enhanced by ion bombardment at impact energy of <100 eV. In this way, homogeneous, good quality films were deposited at rates up to 1800 Angströms/min, and there is a well justified hope that this rate can be further increased.

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