Journal ArticleDOI
A MNDO-Study of Solvent Free and Solvated Dimeric Lithium Ion Pairs of Acetaldoxime. Models for Dimeric Aggregates of Lithiated Oxime Ethers
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In this paper, the adequacy of MNDO was evaluated critically with reference to ab initio results, including excessive charge localization, the breakdown of the pseudo-π conjugation within the ligands, and orbital orientation towards the cation.Abstract:
Cyclic and stack-type structures of solvent-free and solvated dimeric lithium ion pairs of isomeric carbanions of acetaldoxime were investigated as models for lithiated oxime ethers. The adequacy of MNDO is evaluated critically with reference to ab initio results. Severe overestimation of the pyramidalization at the carbanionic center and insufficient carbon lone-pair—lithium core repulsion are found to cause the following artifacts: excessive charge localization, the breakdown of the pseudo-π conjugation within the ligands, and orbital orientation towards the cation; standard MNDO calculations yield entirely unacceptable results. A simple method is proposed to counteract some of these deficiencies and results thus obtained are in significantly better agreement with ab initio data. Solvated cyclic ( C i symmetric) dimers were found to be the most important aggregated species; they are preferred over bis -solvated monomeric ion pairs at the MNDO level. The magnitudes of the relative energies are such that a definitive conclusion regarding the predominance of monomeric or dimeric aggregates cannot be made. Mechanistic implications with regard to the experimentally observed syn -axial entry of electrophiles into configurationally fixed lithiated oxime ethers are discussed.read more
Citations
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Book ChapterDOI
Structures of Organonitrogen—Lithium Compounds: Recent Patterns and Perspectives in Organolithium Chemistry
TL;DR: The structure and properties of complexed organolithium compounds are discussed in this paper, with a focus on simple amides (R 2 NLi) and simple iminolithium (R 1 NLi).
Journal ArticleDOI
Ab Initio and Semiempirical Study of the Effect of Ethereal Solvent on Aggregation of a Lithium Enolate
TL;DR: In this paper, the effect of dimethyl ether solvation on aggregated forms of the lithium enolate of acetaldehyde (CH2CHOLi)n(Me2O)x, n = 1−4, x = 0−4 was studied theoretically.
Journal ArticleDOI
Effect of Polydentate Donor Molecules on Lithium Hexamethyldisilazide Aggregation: An X-ray Crystallographic and a Combination Semiempirical PM3/Single Point ab Initio Theoretical Study
TL;DR: In this article, the PM3 calculations were used to locate minima for a variety of possible structures for the ligands N, N,N,N', N'-tetramethylethylenediamine and 1,2-dimethoxyethane.
Journal ArticleDOI
Toward Solution-State Structure. A 6Li,1H HOESY NMR, X-ray Diffraction, Semiempirical (PM3, MNDO), and ab Initio Computational Study of a Chiral Lithium Amide
TL;DR: In this paper, a chiral lithium amide (lithium (2-methoxy-(R)-1-phenylethyl)((S)-1-, 1-phenylthyl)amide, 3) using the solid-state structure as a reference geometry showed that there were only small differences between the X-ray and ab initio and PM3 calculated structures.
Journal ArticleDOI
Stereocontrolled Synthesis of Cyclic Ethers by Intramolecular Hetero-Michael Addition. 6. A Computational Study of the Annelation to 2,3-Disubstituted Tetrahydropyrans
TL;DR: In this paper, a computational study at the ab initio level of the cyclization of (E)- and (Z)-7-hydroxy-4-substituted-2,3-unsaturated esters leading to 2,3disubstitized tetrahydropyrans has been performed.
References
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Journal ArticleDOI
Ground States of Molecules. 38. The MNDO Method. Approximations and Parameters
Michael J. S. Dewar,Walter Thiel +1 more
Journal ArticleDOI
Ground States of Molecules. 39. MNDO Results for Molecules Containing Hydrogen, Carbon, Nitrogen, and Oxygen
Michael J. S. Dewar,Walter Thiel +1 more
Journal ArticleDOI
Hydration of the alkali ions in the gas phase. Enthalpies and entropies of reactions M+(H2O)n-1 + H2O = M+(H2O)n
I. Dzidic,Paul Kebarle +1 more
Book ChapterDOI
X-ray structural analyses of organolithium compounds
TL;DR: In this article, the X-ray structural analyses of organolithium compounds have been discussed, and a number of mixed-metal organometallic compounds with a single contact between lithium and a carbon atom have been characterized.
Journal ArticleDOI
Microwave Spectra and Structure of Dimethyl Ether
TL;DR: In this paper, the microwave spectra of six isotopic species of dimethyl ether were investigated from 8-48 Gc and the conformation of the methyl groups was determined from the (CH2D) (CH3)O species.
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