Carbon compounds, heterocyclic/cyclic

The analytical data obtained, particularly by the PUMA mass spectrometer on board Vega 1 during the flyby, indicate the presence of a large number of linear and cyclic carbon compounds, such as olefins, alkynes, imines, nitriles, aldehydes and carboxylic acids, but also heterocyclic compounds (pyridines, pyrroles, purines and pyrimidines) and some benzene derivatives no amino acids, alcohols or saturated hydrocarbons are, however, present (Kissel and Krueger, 1987 Krueger and Kissel, 1987). 

The Rh complex 72 shown in Fig. 35 was obtained by simple addition of the N-heterocyclic carbon(O) ligand to [Rh(p-Cl)(CO)2l2 in THF solution [103,104]. The transition metal complexes 73 and 74 of the all carbon four-membered cyclic ligand shown in Fig. 15 were prepared by adding the rhodium or iridium compounds [M(p-Cl)(cod)]2 to the freshly generated allene at 20° C in THF solution [105, 106]. The cod ligand can easily be replaced by admitting CO at room temperature to THF solutions of the complexes to give 75 and 76, respectively, as shown in Fig. 35. 

Carbon compounds can be classified according to their molecular framework as acyclic (not cyclic), carbocyclic (containing rings of carbon atoms), or heterocyclic (containing at least one ring atom that is not carbon). They may also be classified according to functional group (Table 1.6). 

Cyclic compounds played an important role in organic chemistry from its very beginning. Both rings with carbon-only skeletons (cyclic hydrocarbons and their derivatives) and with heteroatom skeletons (an endless diversity of heterocycles) have been known for a long time. The discovery of the cyclic structure of benzene is a landmark in the history of chemistry, and it has been followed by a rapid progress in this branch of science, even in the nineteenth century, when elemental analysis and the chemist s intuition and imagination were the most important research tools. 

Heterocyclic compounds are cyclic structures which contain an atom other than carbon as part of a ring system. Heteroaromatic compounds are a group of these which possess a cyclic conjugated system that can satisfy the (4 + 2)n electron rule and thus have some aromatic stabilization. 

Some amines are heterocyclic compounds (or heterocycles)—cyclic compounds in which one or more of the atoms of the ring are heteroatoms. A heteroatom is an atom other than carbon. The name comes from the Greek word heteros, which means different. A variety of atoms, such as N, O, S, Se, P, Si, B, and As, can be incorporated into ring stmctures. 

Heterocyclic compounds are cyclic compounds containing one or more atoms of elements other than carbon—commonly sulfur, oxygen, or nitrogen—in then-ring structure. Heterocyclic compounds constitute an important class of organic... 

Heterocyclic compounds are cyclic compounds in which one or more atoms other than carbon (usually nitrogen, oxygen, or sulfur) are present in the ring. An example is pyridine, C5H5N, a colorless liquid with an unpleasant odor, which is among the products of distilling coal. The electronic structure of pyridine can be described as a hybrid of several valence-bond structures ... 

The electronic structures of a range of compounds (acyclic, cyclic and heterocyclic) have been explored by DFT calculations. It was more specifically shown that the charge of the divalent carbon compound exhibit the main contribution to the tr basicity (related to the a donor strength) followed by the nature of the atom a to the divalent carbon. This effect has been shown to propagate along the chain. The nature of the n system is less related to the structural nature of the molecules but fits well with the description of the n molecular orbitals which explain both the n acidity and the n basicity. 

CycUc ethers are members of a class of cycloalkanes in which one or more carbons have been replaced by a heteroatom—in this case, oxygen. (A heteroatom is defined as any atom except carbon and hydrogen.) Cyclic compounds of this type, called heterocycles, are discussed more fully in Chapter 25. 

Not all cyclic compounds are hydrocarbons Many substances include an atom other than carbon called a heteroatom (Section 1 7) as part of a ring A ring that contains at least one heteroatom is called a heterocycle, and a substance based on a heterocyclic ring is... 

Cyclic compounds that contain at least one atom other than carbon within their ring are called heterocyclic compounds, and those that possess aromatic stability are called het erocyclic aromatic compounds Some representative heterocyclic aromatic compounds are pyridine pyrrole furan and thiophene The structures and the lUPAC numbering system used m naming their derivatives are shown In their stability and chemical behav lor all these compounds resemble benzene more than they resemble alkenes... 

HETCOR (Section 13 19) A 2D NMR technique that correlates the H chemical shift of a proton to the chemical shift of the carbon to which it is attached HETCOR stands for heteronuclear chemical shift correlation Heteroatom (Section 1 7) An atom in an organic molecule that IS neither carbon nor hydrogen Heterocyclic compound (Section 3 15) Cyclic compound in which one or more of the atoms in the nng are elements other than carbon Heterocyclic compounds may or may not be aromatic... 

Heterocyclic compound (Section 3.15) Cyclic compound in which one or more of the atoms in the ring are elements other than carbon. Heterocyclic compounds may or may not be aromatic. 

A heterocycle is a cyclic compound that contains atoms of two or more elements in its ring, usually carbon along with nitrogen, oxygen, or sulfur. Heterocyclic amines are particularly common, and many have important biological properties. Pyridoxal phosphate, a coenzyme sildenafil (Viagra),... 

Topics in Heterocyclic Chemistry presents critical accounts of heterocyclic compounds (cyclic compounds containing at least one heteroatom other than carbon in the ring) ranging from three members to supramolecules. More than half of the more than 10000 compounds hsted in Chemical Abstracts are hete-rocychc compounds. The branch of chemistry deahng with these heterocyclic compounds is called heterocyclic chemistry, which is the largest branch of chemistry and as such the chemical hterature appearing every year as research papers and review articles is vast and can not be covered in a single volume. 

Intramolecular arylation of G-H bonds gives cyclic aromatic compounds. In this intramolecular arylation, the carbon-palladium cr-bond is first formed by the oxidative addition of Pd(0) species and then the resulting electrophilic Pd(n) species undergoes the intramolecular G-H bond activation leading to the formation of the palladacycle, which finally affords the cyclic aromatic compounds via reductive elimination.87 For example, the fluoroanthene derivative is formed by the palladium-catalyzed reaction of the binaphthyl triflate, as shown in Scheme 8.88 This type of intramolecular arylation is applied to the construction of five- and six-membered carbocyclic and heterocyclic systems.89 89 89 ... 

As far as the polymerisation of heterocyclic compounds with one hetero-atom is concerned (cyclic ethers and their analogues) there seems little doubt at present that the propagation involves a displacement at the positive propagating centre. The ring which is part of this -onium ion is opened between the charged atom and a carbon atom next to it, and this becomes attached to the hetero-atom of the monomer ... 

The cyclizahon of amino alcohols should be an attractive method for the synthesis of N-heterocyclic compounds, mainly because they can be obtained in a single step and without the generation of wasteful byproducts. Carbon-nitrogen bond formation catalyzed by Cp lr complexes has been extended to the synthesis of N-hetero-cyclic compounds by the cyclization of amino alcohols. 

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