The E2C mechanism in elimination reactions. IX. Re-examination of the olefin-like transition-state

1983 ◽  
Vol 36 (9) ◽  
pp. 1667 ◽  
Author(s):  
DM Muir ◽  
AJ Parker
Keyword(s):  
Double Bond ◽  
Transition State ◽  
Valence Bond ◽  
Large Degree ◽  
Apparent Lack ◽  
Bond Model ◽  
Leaving Group ◽  
Elimination Reactions ◽  
Kinetics Of ◽  
Bond Character

The kinetics and product olefins arising from E2C-like elimination reactions of secondary bromides and tosylates having various alkyl and conjugating substituents at Cα and Cβ are re-examined in the light of the theoretical Pross-Shaik valence-bond model and the apparent lack of a β-phenyl effect. Comparison of the effect of substituents at Cα and Cβ shows that whilst there are differences in reactivity and products of E2C reactions there is also a large degree of double-bond character in the transition state. There is a good correlation between the kinetics of E2C reactions and the double-bond stabilization energy arising from both alkyl and conjugating substituents. Contributing valence-bond structures, giving asymmetry and partial charge at Cα and Cβ appear to vary in importance according to leaving group and substituent type.

Ab initio studies on amides: triformamide

1981 ◽  
Vol 34 (1) ◽  
pp. 7
Author(s):  
L Radom ◽  
NV Riggs
Keyword(s):  
Double Bond ◽  
Transition State ◽  
Ab Initio ◽  
Internal Rotation ◽  
Direct Observation ◽  
Ground State ◽  
Basis Set ◽  
Model Transition ◽  
Bond Character ◽  
Complete Optimization

Complete optimization with the STO-3G basis set of the geometries of the planar ground-state conformers of the (unknown) triformamide molecule predicts that the E,E,E conformer will be more stable than the E,Z,Z conformer by 12.6 kJ mol-1 (or 42.3 kJ mol-1 by energy evaluations with the 4-31G basis set). These differences make direct observation of the E,Z,Z-conformer unlikely. Corresponding optimization of a model transition state for the conversion of the E,Z,Z into the E,E,E conformer suggests that the barrier to internal rotation is low with a calculated height of 33 kJ mol-1 (24 kJ mol-1 when evaluated with the 4-31G basis set). Successive formyl substitution in ammonia, represented by the series of molecules formamide, diformamide (formimide) and triformamide, leads to decreasing double-bond character in the N-C bonds as reflected in increasing N-C bond lengths, decreasing Mulliken π-overlap populations and decreasing barriers to rotation. Extension of the results for these three molecules suggests that the (known) triacetamide molecule has a non-planar E,E,E-type structure as is consistent with the observation of a single signal in its 1H n.m.r. spectrum.

Investigating the Resonance in Nitric Acid and the Nitrate Anion Based on a Modern Bonding Analysis

2018 ◽  
Vol 71 (4) ◽  
pp. 227 ◽  
Author(s):  
Malte Fugel ◽  
Florian Kleemiss ◽  
Lorraine A. Malaspina ◽  
Rumpa Pal ◽  
Peter R. Spackman ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Double Bond ◽  
Theoretical Calculations ◽  
Valence Bond ◽  
Nbo Analysis ◽  
Nitrate Anion ◽  
Resonance Structures ◽  
Bonding Analysis ◽  
Experimental Electron Density ◽  
Bond Character

The nitrate anion, NO3−, is often regarded as a textbook example for the very fundamental concept of resonance. Usually, three equivalent resonance structures with one N–O double bond and two N–O single bonds are considered. Consequently, each of the three N–O bonds should have a partial double bond character. In this study, we analyse the resonance in NO3− in comparison with the related species HNO3 and FNO3 by applying a combination of the Quantum Theory of Atoms in Molecules (QTAIM), a natural bond orbital (NBO) analysis, the electron localizability indicator (ELI), and valence bond (VB) calculations. Despite the fundamental importance of nitrate salts and nitric acid for the environment, chemistry, and industry, a bonding analysis is absent from the literature so far. The classical resonance structures are clearly reflected by the bond analysis tools, but are not the only contributions to the bonding situation. The resonance in HNO3 and FNO3 is greatly perturbed by the hydrogen and fluorine atoms. In addition to theoretical calculations, experimental electron density and wave function refinements were carried out on a KNO3 crystal.

scholarly journals Force-modulated reductive elimination from platinum(ii) diaryl complexes

2021 ◽  
Author(s):  
Yichen Yu ◽  
Chenxu Wang ◽  
Liqi Wang ◽  
Cai-Li Sun ◽  
Roman Boulatov ◽  
...  
Keyword(s):  
Transition State ◽  
Reductive Elimination ◽  
Mechanical Force ◽  
Elimination Reactions

The influence of mechanical force on the rates of model reductive elimination reactions depends on the structure of the force-transducing ligand and provides a measure of geometry changes upon reaching the transition state.

THE ALKALINE CLEAVAGE OF o-NITROBENZYLTRIMETHYLSILANE SOLVENT EFFECTS IN THE DIOXANE–WATER SYSTEM

1963 ◽  
Vol 41 (6) ◽  
pp. 1525-1530 ◽  
Author(s):  
H. R. Allcock
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Water System ◽  
Solvent Polarity ◽  
High Water ◽  
Aqueous Dioxane ◽  
Alkaline Cleavage ◽  
Rate Of Reaction ◽  
Kinetics Of

The kinetics of alkaline cleavage of o-nitrobenzyltrimethylsilane were examined in aqueous dioxane media. At high water concentrations, increases in solvent polarity retard the cleavage, as required by a mechanism involving charge dispersion in the transition state. At high dioxane concentrations, solvent polarity increases are accompanied by increases in the rate of reaction, a result which may reflect association between the solvent components.

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