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Halogenated Aromatic Compounds
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
Hundreds of millions of pounds of alkyl halides such as chloroform and hexachloroethane are produced annually in the U.S. alone. In 1978, the U.S. produced 11 × 109 lb of dichloroethane (Weisburger, 1981). Vinyl halides such as dichloroethylene and vinyl chloride are also produced in massive amounts. Some alkyl halides such as chloral hydrate (“knock-out drops”), halothane (anesthetic), and chloroform can have deleterious effects on the nervous system. Metabolites of alkyl halides and vinyl halides are most often responsible for liver and kidney toxicity as well as carcinogenic effects.
Elimination Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A vinyl halide is an alkene where a halogen atom is directly attached to one of the sp2-hybridized carbon atoms of the C=C unit. Another alkene product is possible in the elimination reaction of 1,2-dibromopentane, via loss of the hydrogen atom β- to the bromine on C2. What is this product and what is an explanation as to why 1-bromopent-1-ene is formed preferentially?
Structural characterization of ((9-fluorenylidene) (ferrocenyl)methyl)palladium iodide as the catalytic intermediate in the synthesis of 9-(ferrocenyl (ferrocenylethynyl)methylene)-9H-fluorene
Published in Journal of Coordination Chemistry, 2022
Structurally characterized cis-bisphosphino vinyl palladium halide complexes are limited to one example in which a dppe fragment stabilizes a PdBr species in a meso-porphyrin position [20]. Further vinyl halide complexes are reported in their trans-P,P-configuration, due to the higher stability of the complex, making 13 a rare example of a palladium complex of this type in this geometry. The square planar coordination environment is defined by the geometric properties of the dppf backbone structure, enforcing an P–Pd–P angle of 97.4°, consequently reducing the C−Pd–I angle to 87.6° (Figure 3). The planar PdP2 entity is slightly tilted towards the dppf axis by τ = 27.8°, due to a rotation of the organometallic backbone out of an ideal syn-periplanar (eclipsed) conformation by 34.2(5)°. An orthogonal plane intersection between the PdP2 and the fluorenylidene ligand's C=C−CFc entity of 87.8° is required to reduce steric interactions between adjacent ligands.
A quantum mechanical explanation of the structure of vinyl cation based on a CASSCF/CASMP2 study
Published in Molecular Physics, 2020
Panayiotis C. Varras, Michael G. Siskos, Panagiotis S. Gritzapis
The vinyl cation has been the subject of numerous theoretical ab-initio [1–14] and DFT [15] studies. It is one of the simplest carbocations playing an important role in the mechanism of organic reactions, it can be formed for example during the protonation of ethyne and produced photochemically from the photolysis of the corresponding vinyl halide. Its occurrence in the interstellar medium [16,17] has attracted the interest of astronomers and its electronic structure has intrigued many chemists and the controversy about the stability of its two structures, the classical and the non-classical one (Figure 1) has now been settled both theoretically and experimentally [18–20], with the non-classical or bridged structure being the most stable one. Amongst the latest calculations, Sharma’s et al. paper [12] includes high level CCSD(T) computations by fitting a potential energy surface (PES) to the calculated energy values, using a many-body cluster expansion thus producing a full dimensional semi-global PES validating that the bridged structure is the most stable one. Also, the use of high correlated ab-initio methods (CCSD(T), BD(T) and CBS-APNO) along with very large basis sets by Psciuk et al. [13] reconfirmed all previous theoretical calculations and predict an electronic energy range for the difference in the stabilities between the two cations from 3.6 up to 3.8 kcal/mol, while the corresponding electronic activation energies lie between 0.05 and 0.13 kcal/mol.
Pd@GO/Fe3O4/PAA/DCA: a novel magnetic heterogeneous catalyst for promoting the Sonogashira cross-coupling reaction
Published in Journal of Coordination Chemistry, 2019
Mansoureh Daraie, Majid M. Heravi, Shaghayegh Sadat Kazemi
Sonogashira reaction is one of the most important and powerful methods for CC bond formation involving the cross coupling between terminal sp hybridized carbon of an alkyne with a sp2 carbon of an aryl or vinyl halide (or triflate) [9]. The classic Pd-catalyzed Sonogashira cross reaction involves the reaction of a halide and a terminal alkyne in the presence of Pd(II) salts such as chloride or acetate and ligands such as phosphines and phosphates, copper salt (as co-catalyst) and an amine to form an aryl acetylene under anaerobic conditions [10, 11]. The products obtained from this reaction can be used for the synthesis of substituted alkynes [7] in the total synthesis of several natural products [12], pharmaceutical complex molecules [13], polymeric and optical materials [14].