Heterocycles Heteroatoms in Cyclic Organic Compounds

Chapter 25 HETEROCYCLES HETEROATOMS IN CYCLIC ORGANIC COMPOUNDS... 

Atoms other than carbon and hydrogen that appear in organic compounds are called heteroatoms. Cyclic organic compounds that contain one or more heteroatoms are called heterocycles. Heterocyclic compounds are the largest class of organic compounds and can be either aromatic (such as pyridine, pyrrole, and furan) or nonaromatic (such as piperidine, pyrrolidine, and tetrahydrofuran). 

Cyclic organic compounds are classified as carbocycles or as heterocycles. CarbocycJic rings contain only carbon atoms, but heterocyclic rings contain one or more different atoms in addition to carbon. Nitrogen, oxygen, and sulfur are the most common heteroatoms. 

Heterocycles are cyclic organic compounds in which one or more carbon atoms is replaced by heteroatoms, atoms other than CorH. 

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... 

Organic chemistry is the study of carbon (C) compounds, all of which have covalent bonds. Carbon atoms can bond to each other to form open-chain compounds, Fig. 1.1(a), or cyclic (ring) compounds, Fig. 1.1(c). Both types can also have branches of C atoms, Fig. 1.1(b) and (d). Saturated compounds have C atoms bonded to each other by single bonds, C—C unsaturated compounds have C s joined by multiple bonds. Examples with double bonds and triple bonds are shown in Fig. 1.1(c). Cyclic compounds having at least one atom in the ring other than C (a heteroatom) are called heterocyclics, Fig. 1.1 (/). The heteroatoms are usually oxygen (O), nitrogen (N), or sulfur (S). 

A coirpound does not have to be a hydrocarbon to be aromatic. Many heterocyclic compounds are aromatic. A heterocyclic compound is a cyclic compound in which one or more of the ring atoms is an atom other than carbon. The atom that is not carbon is called a heteroatom. The name comes from the Greek word heteros, which means different. The most common heteroatoms encountered in organic compounds are N, O, and S. 

Nina A. Nedolya was born in Irkutsk (Russia) and educated in organic chemistry at the Irkutsk State University (Diploma 1972, PhD 1982, DSc 1998). From 1995 to 1999 she was associated with Prof. L. Brandsma at the Utrecht University (The Netherlands). In 1999 she obtained her second PhD from the Utrecht University. She is presently Head of the Research Group of Chemistry of Heterocyclic Compounds at A. E. Favorsky Irkutsk Institute of Chemistry. She is the author of over 210 review articles and research papers. She is also one of the inventors for 112 patents. She is interested in the chemistry of polyfunctional unsaturated heteroatomic systems (vinyl, allenyl, and alkynyl ethers and their derivatives, linear and cyclic heteropolyenes, hetero-cumulenes), including synthesis of important heterocycles, particularly pyrroles, thiophenes, thiazoles, imidazoles, dihydrofurans, dihydropyridines, pyridines, quinolines, dihydroazepines, and azepines, based on metallated allenes or alkynes and/or heterocumulenes. 

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. 

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