A MNDO study of planar thioacyl-substituted carbocations

1992 ◽  
Vol 70 (1) ◽  
pp. 111-115 ◽  
Author(s):  
Jack Leon Ginsburg ◽  
Richard Francis Langler ◽  
Raj Kumar Raheja ◽  
Laura Precedo
Keyword(s):  
Gas Phase ◽  
Substituent Effects ◽  
Mndo Method ◽  
Saturation Effect ◽  
Semiempirical Calculations ◽  
Isodesmic Reactions ◽  
Electron Population ◽  
Resonance Saturation ◽  
Carbonium Ions

Relative gas phase stabilities of pairs of planar regioisomeric thioacyl-substituted carbocations have been calculated using the MNDO method. These systems are stabilized by good π donors. The role of S π-electron population as a gauge of substituent effects is examined. Similar results were obtained using isodesmic reactions to gauge substituent effects. Results of this and earlier studies are consistent with the resonance saturation effect. Keywords: semiempirical calculations, carbonium ions.

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.

Semiempirische Rechnungen zum Einfluß des Lösungsmittels auf die Protonierungsenergie des Anilins, des Ammoniaks und einiger aliphatischer Amine

1982 ◽  
Vol 37 (1) ◽  
pp. 46-50
Author(s):  
Jörg Fleischhauer ◽  
Gerhard Raabe
Keyword(s):  
Hydrogen Bonds ◽  
Gas Phase ◽  
Mndo Method ◽  
Semiempirical Calculations ◽  
Specific Interactions

Abstract The MINDO/3- and the MNDO-method have been used to determine the site of protonation of Aniline in the gas phase. We used the results of our semiempirical calculations together with the electrostatic "Solvaton-Model" to study the influence of the solvent on the energetics of the protonation of some amines and the site of protonation in Aniline. Our results indicate that the "Solvaton-Model", although neglecting specific interactions between solvent and solute such as the formation of hydrogen bonds, describes the change of the energy of solvation during the protonation in a rather successful agreement with experimentel results.

scholarly journals The Role of Through-Bond Stereoelectronic Effects in the Reactivity of 3-Azabicyclo[3.3.1]nonanes

2021 ◽  
Author(s):  
Croix Laconsay ◽  
Tyler Rho ◽  
Dean Tantillo
Keyword(s):  
Density Functional Theory ◽  
Hydrochloric Acid ◽  
Density Functional ◽  
Noncovalent Interactions ◽  
Substituent Effects ◽  
Isodesmic Reactions ◽  
Functional Theory ◽  
Stereoelectronic Effects ◽  
Computational Analyses

Hyperconjugation/conjugation through-bond stereoelectronic effects were studied with density functional theory (DFT) in the context of 3-azabicyclo[3.3.1]nonanes to unravel puzzling differences in reactivity between a vinylogous chloride (4) and a vinylogous ester (5). These compounds—whose structures differ only by one substituent—were found to display strikingly different reactivities in hydrochloric acid by Risch and co-workers (J. Am. Chem. Soc. 1991, 113, 9411–9412). Computational analyses of substituent effects, noncovalent interactions, natural bond orbitals, isodesmic reactions, and hydration propensities lead to a model for which the role of remote, through-bond stereoelectronic effects is key to explaining 4 and 5’s diverging reactivity.

An MNDO study of substituent effects in carbocations: the unimportance of inductive effects

1986 ◽  
Vol 64 (3) ◽  
pp. 532-538 ◽  
Author(s):  
Amin Mohamed Aissani ◽  
James Clayton Baum ◽  
Richard Francis Langler ◽  
Jack Leon Ginsburg
Keyword(s):  
Gas Phase ◽  
Substituent Effects ◽  
Simple Groups ◽  
Special Importance ◽  
Isodesmic Reactions ◽  
Polarization Effects ◽  
Inductive Effects ◽  
Mndo Calculations ◽  
A Site

Stabilization effects for both saturated and unsaturated substituents were examined using MNDO calculations. (By "saturated substituents" we mean to imply that the substituent is attached to C+ by sp3 carbon, whether or not the substituent has a site of unsaturation at some point remote from the carbocationic center.) Relative gas phase stabilities of regioisomeric carbocations have been calculated. For simple groups, directly bound to [Formula: see text], π donation, σ donation, and polarization effects are found to be important. Saturated-substituent stabilization effects are examined by means of reaction enthalpies for isodesmic reactions between the appropriate neutral molecules and [Formula: see text]. Traditional analyses of substituent effects based solely on inductive effects for saturated groups have little or no significance. Inductive effects have no special importance in determining saturated substituent stabilization effects on carbocations.

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.

On the Structure of Lead(II) Complexes in Aqueous Solutions. I. Trinuclear Clusters

1995 ◽  
Vol 60 (4) ◽  
pp. 527-536 ◽  
Author(s):  
Martin Breza ◽  
Alena Manová
Keyword(s):  
Quantum Chemistry ◽  
Aqueous Solutions ◽  
Electronic Structures ◽  
Mndo Method ◽  
Model Systems ◽  
Trinuclear Clusters ◽  
The Stability ◽  
Semiempirical Mndo

Using semiempirical MNDO method of quantum chemistry the optimal geometries and corresponding electronic structures of [Pb3(OH)n]6-n model systems as well as of their hydrated [Pb3(OH)n(H2O)8-n]6-n analogues (n = 4, 5) are investigated. The most stable trinuclear lead(II) complexes present in aqueous solutions correspond to cyclo-(μ3-OH)(μ2-OH)3Pb32+, Pb(μ-OH)2Pb(μ-OH)2Pb2+, cyclo-(μ3-OH)2(μ2-OH)3Pb3+, Pb(OH)(μ-OH)2Pb(μ-OH)Pb(OH)+ and Pb(OH)(μ-OH)2Pb(μ-OH)2Pb+ systems. The key role of OH bridges (by vanishing direct Pb-Pb bonds) on the stability of individual isomers is discussed.

scholarly journals The role of radiolysis in the modelling of C2H4O2 isomers and dimethyl ether in cold dark clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 3414-3424
Author(s):  
Alec Paulive ◽  
Christopher N Shingledecker ◽  
Eric Herbst
Keyword(s):  
Gas Phase ◽  
Dimethyl Ether ◽  
Recent Observation ◽  
Cosmic Ray ◽  
Thermal Method ◽  
Dark Clouds ◽  
Ice Surface ◽  
Dust Grain ◽  
Complex Organic

ABSTRACT Complex organic molecules (COMs) have been detected in a variety of interstellar sources. The abundances of these COMs in warming sources can be explained by syntheses linked to increasing temperatures and densities, allowing quasi-thermal chemical reactions to occur rapidly enough to produce observable amounts of COMs, both in the gas phase, and upon dust grain ice mantles. The COMs produced on grains then become gaseous as the temperature increases sufficiently to allow their thermal desorption. The recent observation of gaseous COMs in cold sources has not been fully explained by these gas-phase and dust grain production routes. Radiolysis chemistry is a possible non-thermal method of producing COMs in cold dark clouds. This new method greatly increases the modelled abundance of selected COMs upon the ice surface and within the ice mantle due to excitation and ionization events from cosmic ray bombardment. We examine the effect of radiolysis on three C2H4O2 isomers – methyl formate (HCOOCH3), glycolaldehyde (HCOCH2OH), and acetic acid (CH3COOH) – and a chemically similar molecule, dimethyl ether (CH3OCH3), in cold dark clouds. We then compare our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and B1-b.

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