An MNDO study of sulfenium ions

1983 ◽  
Vol 61 (3) ◽  
pp. 589-593 ◽  
Author(s):  
Jack Leon Ginsburg ◽  
Richard Francis Langler
Keyword(s):  
Gas Phase ◽  
Substituent Effects ◽  
Frontier Orbital ◽  
Relative Stabilities ◽  
Ion Formation ◽  
Orbital Analysis

An MNDO study has been carried out on a variety of substituted sulfenium ions and sulfides. Relative stabilities in the gas phase have been calculated for several pairs of regioisomeric sulfenium ions. It is shown that sulfenium ions are stabilized by π-donors and that the substituent electronegativity is not an important factor. The potential implications of this result for the mechanism by which chlorosulfonium cations are converted into sulfenium ions in solution is discussed. Substituent effects on the energetics of sulfenium ion formation from sulfides have been obtained. It is shown that these effects also are related to the substituent's π-donating ability. A frontier-orbital analysis of selected sulfenium ions has been done and is discussed.

Substituent effects on the optical properties of naphthalenediimides: A frontier orbital analysis across the periodic table

2015 ◽  
Vol 37 (2) ◽  
pp. 304-313 ◽  
Author(s):  
Joshua R. Mulder ◽  
Célia Fonseca Guerra ◽  
J. Chris Slootweg ◽  
Koop Lammertsma ◽  
F. Matthias Bickelhaupt
Keyword(s):  
Optical Properties ◽  
Periodic Table ◽  
Substituent Effects ◽  
Frontier Orbital ◽  
Orbital Analysis

Electron affinities of substituted nitrobenzenes

1989 ◽  
Vol 67 (4) ◽  
pp. 603-610 ◽  
Author(s):  
S. Chowdhury ◽  
H. Kishi ◽  
G. W. Dillow ◽  
P. Kebarle
Keyword(s):  
High Pressure ◽  
Electron Transfer ◽  
Gas Phase ◽  
Substituent Effects ◽  
Negative Ions ◽  
Radical Anions ◽  
Electron Affinities ◽  
Frontier Orbital ◽  
Data Set ◽  
Qualitative Discussion

The electron affinities of 14 substituted nitrobenzenes including nitrobiphenyls were determined by measurement of electron transfer equilibria [1] in the gas phase with a pulsed high pressure mass spectrometer: A− + B = A + B− [1]. These data, when combined with previous determinations from this laboratory, lead to electron affinities for 35 substituted nitrobenzenes and provide a comprehensive data set for the examination of substituent effects. The data are used to derive Taft gas-phase substituent parameters. A qualitative discussion based on frontier orbital molecular theory examines the substituent effect on the benzene and nitrobenzene LUMOs. The lifetimes for electron autodetachment from excited nitrobenzene negative ions, (A−)*, studied earlier by Christophorou, are examined in light of the present electron affinity data. Keywords: electron affinities, substituent effects, frontier orbital treatment, electron autodetachment from nitrobenzene radical anions.

Theoretical studies of SN2 transition states. Substituent effects

1982 ◽  
Vol 60 (11) ◽  
pp. 1291-1294 ◽  
Author(s):  
Saul Wolfe ◽  
David John Mitchell ◽  
H. Bernhard Schlegel
Keyword(s):  
Gas Phase ◽  
Transition States ◽  
Substituent Effects ◽  
Orbital Interaction ◽  
Frontier Orbital ◽  
Orbital Interactions ◽  
Pyramidal Inversion ◽  
New Type ◽  
Constraint Effects ◽  
And Inversion

Similar substituent and angular constraint effects are noted for pyramidal inversion at tricoordinate nitrogen and inversion at a carbon centre undergoing an SN2 displacement reaction. The former process has been analyzed successfully by a quantitative PMO analysis which focuses on the frontier orbital interactions between X and NH2 in the planar and pyramidal structures of X—NH2 molecules having X = F, CH3, CHO. Based on total energy calculations at the 6-311G*//4-31G level, the effects of X upon the rates of the gas phase SN2 reactions F− + XCH2F → XCH2F + F− are found to be [Formula: see text]. Taking the treatment of nitrogen inversion as a precedent, the origin of this trend has been examined by a quantitative PMO analysis which focuses on the frontier orbital interactions between X and CH2F2− in the transition states, and between X and CH2F in the reactants. This has revealed that the rate enhancement associated with an α-carbonyl substituent in these SN2 reactions can be related to the presence of a stabilizing orbital interaction of a new type in the transition state, coupled to an exceptionally low destabilizing orbital interaction.

Rapid Evaluation of Suitable Substrates with High Affinity to Artificial Caffeine Receptors by MS Based Techniques

2005 ◽  
Vol 60 (10) ◽  
pp. 1077-1082 ◽  
Author(s):  
Daniela Mirk ◽  
Heinrich Luftmann ◽  
Siegfried R. Waldvogel
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Collision Induced Dissociation ◽  
Rapid Evaluation ◽  
Tandem Mass ◽  
Binding Affinities ◽  
Electrospray Tandem Mass Spectrometry ◽  
Relative Stabilities ◽  
Receptor Complexes ◽  
High Affinity

A modification of our triphenylene ketal based receptor facilitates electrospray tandem mass spectrometry investigations. Binding affinities of eleven potential substrates, e.g. caffeine and other xanthine alkaloids, are probed in the gas phase with collision induced dissociation. The relative stabilities of the substrate-receptor complexes are rapidly determined and the findings are correlated with the corresponding results in solution.

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