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.

Computational study of substituent effects on gas-phase stabilities of Meisenheimer complexes

2015 ◽  
Vol 93 (12) ◽  
pp. 1327-1334 ◽  
Author(s):  
Kazuhide Nakata ◽  
Mizue Fujio ◽  
Hans-Ullrich Siehl ◽  
Yuho Tsuno
Keyword(s):  
Gas Phase ◽  
Narrow Range ◽  
Computational Study ◽  
Substituent Effects ◽  
Orbital Interaction ◽  
Conjugation System ◽  
Isodesmic Reactions ◽  
Meisenheimer Complexes ◽  
Stabilization Energies ◽  
Respective Species

The total stabilization energies (TSEs) and anion stabilization energies (ASEs) of ring-substituted (X-) Meisenheimer complexes featuring two NO2 groups in the ring were determined using appropriate isodesmic reactions. The structures and energies of respective species were calculated at the B3LYP/6–311+G(2d,p) level of theory. Ten series of substituent effects were examined by varying substituent Y, which is connected to the sp3 carbon of the ring. The substituent effects were successfully analyzed using an extended Yukawa–Tsuno equation, [Formula: see text]. The r− values for the TSEs were identical to those for the ASEs, whereas the s values for the TSEs were significantly different from those for the ASEs. This shows that the effect of neutral species contributes to the s values of the TSEs. The r− and s values for the ASEs of all Meisenheimer complexes were distributed in a narrow range because substituent Y was insulated from the π-conjugation system. The r− values were large and the s values were small. This shows that the r− and s values were independent of each other and that the extended three-term Yukawa–Tsuno equation was intrinsic for substituent-effect analyses of anions. Although the variation was not substantial, the change in the r− values was clearly explained by the orbital interaction between substituent Y and the π-conjugation system. The r− values exhibited a good correlation with the bond lengths between the ring and the 4-NO2 group among all Meisenheimer complexes and benzylic anions. These facts provide a physical meaning: the r− value is a parameter that reveals the degree of the additional π interactions between the electron-withdrawing substituents and the π-conjugation systems of the ring.

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.

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.

Dimer formation of NO ligands in the gas-phase halide ion clusters X−(NO) enhanced by a frontier orbital interaction

2000 ◽  
Vol 323 (1-2) ◽  
pp. 155-159 ◽  
Author(s):  
Kenzo Hiraoka ◽  
Tomoyuki Iino ◽  
Daisuke Eguchi ◽  
Takayuki Mizuno ◽  
Shinichi Yamabe
Keyword(s):  
Gas Phase ◽  
Orbital Interaction ◽  
Frontier Orbital ◽  
Dimer Formation ◽  
Ion Clusters

scholarly journals Computational study of the substituent effects on the gas-phase stabilities of phenylboranylmethyl anions

2017 ◽  
Vol 89 (11) ◽  
pp. 1685-1694
Author(s):  
Kazuhide Nakata ◽  
Mizue Fujio
Keyword(s):  
Gas Phase ◽  
Benzene Ring ◽  
Computational Study ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Nbo Analysis ◽  
Side Chain ◽  
Isodesmic Reactions ◽  
Effect Analysis ◽  
Orbital Interactions

AbstractThe relative gas-phase stabilities of ring-substituted phenylboranylmethyl anions were computationally determined using isodesmic reactions. The energies of species included in the reactions were calculated at the B3LYP/6-311+G(2d,p) level of theory. The obtained substituent effects were analyzed by the extended Yukawa-Tsuno equation, and unexpectedly substantial r− (0.59) and s (0.65) values were found for the fully-optimized planar anion. The substantial through-resonance effect quantified by the r− value was observed, although it is not possible to draw a canonical form in which the negative charge is delocalized on the benzene ring. Substituent effects were also analyzed for the anions in which the dihedral angle (φ) between the side chain plane and the benzene ring was fixed. The r− value decreased significantly by changing the φ from 0° to 90°, while the s value changed little. NBO analyses revealed that the r− value is proportional to the sum of the π–π* and σ–π* orbital interactions between the side chain and the benzene ring. This fact shows that the through-resonance effect quantified by the r− value is present at all φ, and therefore, the anion cannot become an ideal σ0-reference system. The constant saturation effect quantified by the s value can be explained by the constant charge distributed to the benzene ring. The combination of substituent-effect analysis and NBO analysis successfully revealed the nature of the anion.

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