Heteroatoms aromaticity

A variety of aromatic compounds can be polymerized electrochemically to form a thin polymer filmf 1 -41. Many films involving heteroatom aromatics can be made electrically conducting... 

Intramolecular anodic olefin coupKng reactions involving heteroatomic aromatic rings were used to prepare fused, bicyclic ring skeletons (Scheme 122) [159]. 

In five-membered heterocycles, formally derived from benzene by the replacement of a CH=CH unit by a heteroatom, aromaticity is achieved by sharing four p-electrons, one from each ring carbon, with two electrons from the heteroatom. Thus in pyrrole, where the heteroatom is N, all the ring atoms are sp hybridized, and one sp orbital on each is bonded to hydrogen. To complete the six 7i-electron system the non-hybridized p-orbital of N contributes two electrons (Box 1.9). It follows that the nitrogen atom of pyrrole no longer possesses a lone pair of electrons, and the compound cannot function as a base without losing its aromatic character. 

The results so far suggest that stabilization of the intermediate carbocation by an adjacent heteroatom, aromatic ring or by steric factors stimulates fluorination of a CLH bond by sulfur tetrafluoride. 

Know the meaning of heteroatom, aromatic heterocycle, nonaromatic heterocycle, diazine, azole. 

Group XI Aromatic hydrocarbons, heteroatomic aromatic compounds as well as compounds of Group X, which have additional hydrogen-containing substituents or functions. 

Among the five-membered rings with boron and a second heteroatom, aromaticity is only relevant for anionic systems which are isoelectronic with C5H5. This is the case for only one type of compound, the 1,2-azaborolyl ring (1,2-azaboratole) (42). This anion derives from the neutral l//-l,2-azaborole by abstraction of a proton, as when cyclopentadiene is transformed into the cyclopentadienide. 

Heteroatom Heteroatom Aromatic Rearrangements (Smiles Rearrangement) The... 

Sanford, E.C. Influence of hydrogen and catalyst on distillate yields and the removal of heteroatoms, aromatics, and CCR during cracking of Athabasca bitumen residuum over a wide range of conversions, Energy Fuels 1994,8,1276-1288. 

Resins are generally molecules having aromatic characteristics and contain heteroatoms (N, 0, S, occasionally Ni and V) their molecular weight ranges from 500 to 1000. 

Liquid chromatography is preceded by a precipitation of the asphaltenes, then the maltenes are subjected to chromatography. Although the separation between saturated hydrocarbons and aromatics presents very few problems, this is not the case with the separation between aromatics and resins. In fact, resins themselves are very aromatic and are distinguished more by their high heteroatom content (this justifies the terms, polar compounds or N, S, 0 compounds , also used to designate resins). 

A wide variety of carbocations and carbodications, including those that are aromatically stabilized as well those as stabilized by heteroatoms, were reported in the nearly 200 publications on the topic during my Cleveland years. 

In their reactions with suitable nucleophiles, such as tt-aromatics or heteroatom donor nucleophiles, the readily polarizable linear acylium ions shift a Tt-electron pair to oxygen, bending the ions and developing an empty p-orbital at the carbocationic center. This enables the reaction with aromatics. The acetylation of benzene can be depicted as... 

The NMR spectra of thiazoles show the same behavior as those of aromatic compounds, but the chemical shifts also depend on the two heteroatoms. 

A large group of heterocyclic aromatic compounds are related to pyrrole by replacement of one of the ring carbons p to nitrogen by a second heteroatom Com pounds of this type are called azoles... 

Section 11 23 Huckel s rule can be extended to heterocyclic aromatic compounds Unshared electron pairs of the heteroatom may be used as tt electrons as necessary to satisfy the 4n + 2 rule... 

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... 

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