Search results for "Cyclopentadiene"
showing 9 items of 49 documents
Theoretical Studies on the Mechanism of the Formation of Cyclopentadienes and Dihydropyridazines
2021
A theoretical study of the molecular mechanism of the reaction between N,N-dimethylmethyleneammonium cation and cyclopentadiene.
2001
WHY DIELS-ALDER REACTIONS ARE NON-CONCERTED PROCESSES
2014
ABSTRACT Two exhaustive topological analyses using the Electron Localisation Function (ELF) along the non-polar Diels-Alder reactions of 1,3-butadiene [J. Phys. Chem. A 107 , 6014 (2003)] and cyclopentadiene [Org. Biomol. Chem. 8 , 5495, (2010)] with ethylene established that the bonding changes along these reactions are non-concerted. Herein, the ELF bonding changes along the intramolecular Diels-Alder reaction of 1-( hex-5-enyl)cyclohexa-1,3-diene is analysed. The geometrical restrictions imposed by the tether break the synchronicity in the single bond formation in this non-polar reaction. The present ELF topological analysis along this intramolecular Diels-Alder reaction supports the ear…
ChemInform Abstract: The Chemistry of Unsaturated Nitrogen-Heterocyclic Compounds Containing Carbonyl Groups
2010
Publisher Summary Most hydroxy-substituted azaheteroaromatic compounds exist predominately in the NH/carbonyl tautomeric form, and these compounds have been widely discussed. This chapter provides an overview of azaheteroaromatic compounds and I-azetin-4-ones—these are those azaheterocycles that contain in the ring at least one carbonyl group and one or two nitrogen atoms in the form of C=N or N=N bonds. Many of these compounds are unstable but their importance as reactive intermediates is established, and many of them could be used as synthons in the preparation of pharmacologically active compounds. The chapter describes the free existence of I-azetin-4-one and the nucleophilic substituti…
The Chemistry of Unsaturated Nitrogen–Heterocyclic Compounds Containing Carbonyl Groups
1993
Publisher Summary Most hydroxy-substituted azaheteroaromatic compounds exist predominately in the NH/carbonyl tautomeric form, and these compounds have been widely discussed. This chapter provides an overview of azaheteroaromatic compounds and I-azetin-4-ones—these are those azaheterocycles that contain in the ring at least one carbonyl group and one or two nitrogen atoms in the form of C=N or N=N bonds. Many of these compounds are unstable but their importance as reactive intermediates is established, and many of them could be used as synthons in the preparation of pharmacologically active compounds. The chapter describes the free existence of I-azetin-4-one and the nucleophilic substituti…
DFT Study of the Molecular Mechanism of Lewis Acid Induced [4 + 3] Cycloadditions of 2-Alkylacroleins with Cyclopentadiene
2009
The mechanism of the Lewis acid (AlCl(3)) induced [4 + 3] cycloaddition of 2-methylacrolein with cyclopentadiene (Cp) [ J. Am. Chem. Soc. 2004, 126, 2692] has been examined here through DFT calculations at the MPW1K(DCM)/6-31+G** level. Formation of these seven-membered carbocycles is a domino process that comprises three consecutive reactions. The first one is a polar Diels-Alder reaction that is initialized by the nucleophilic attack of Cp to the beta-conjugated position of acrolein, yielding the formation of the endo and exo [4 + 2] cycloadducts. The corresponding LA-[4 + 2] cycloadduct complexes equilibrate through a skeleton rearrangement with a low free activation energy with two seve…
On the vertical excitation energy of cyclopentadiene
2004
The vertical excitation energy for the lowest valence pi--pi(*) transition of cyclopentadiene is investigated. Using a combination of high-level theoretical methods and spectroscopic simulations, the vertical separation at the ground state geometry is estimated to be 5.43+/-0.05 eV. This value is intermediate between those calculated with coupled-cluster and multireference perturbation theory methods and is about 0.13 eV higher than the observed maximum in the absorption profile.
Imidotungsten(VI) complexes with chelating phenols as ROMP catalysts
2011
Abstract Tungsten(VI) complexes of the type [W(NPh)Cl3(L)] (L = chelating phenolate) were studied as catalyst precursors for ROMP of 2-norbornene, dicyclopentadiene and 5-vinyl-2-norbornene. These compounds form active catalysts when treated by ethyl magnesium bromide. Moreover, polymerisations can be run under ambient atmosphere without complicated inert atmosphere techniques. Synthesis and crystal structure of a new precursor complex [W(NPh)Cl3(LS)] (LS = 2,4-di-tert-butyl-6-(phenylthiomethyl)phenolate) are also described.
A DFT study of the Diels–Alder reaction between methyl acrolein derivatives and cyclopentadiene. Understanding the effects of Lewis acids catalysts b…
2006
Abstract The effects of Lewis acid catalysts based on sulfur containing boron heterocycles on the Diels–Alder reactions of two methyl acroleins with cyclopentadiene have been studied using DFT methods. These reactions take place along highly asynchronous concerted processes. While the reaction with crotonaldehyde leads to the expected endo adduct, the reaction with methacrolein leads to exo one in agreement with the experiments. The catalytic effect can be explained through the analysis of the electrophilicity index (ω) of the reagents, and the molecular structure of the corresponding transition structures.