Heteroatoms Atoms other than carbon

Heterocyclic compounds, or heterocycles, are molecules with rings that contain more than one type of atom they are to be distinguished from carbocycles, which are molecules with rings that contain only carbon atoms. The heterocyclic compounds of greatest interest to medicinal chemists have carbon rings containing one or two heteroatoms— atoms other than carbon. 

Heteroatom Atom other than carbon in the structure of a heterocyclic compound... 

While chemical bonds are represented by lines connecting atoms, electron dot notation is commonly used to represent lone pairs (nonbonding pairs) of electrons. Lone pairs are found on heteroatoms (atoms other than carbon or hydrogen) that do not require bonds with additional atoms to fill their valence shell of eight electrons. For example, atomic... 

Heteroatoms— atoms other than carbon or hydrogen. Common heteroatoms are nitrogen, oxygen, sulfur, phosphorus, and the halogens. 

All heteroatoms (atoms other than carbon and hydrogen) must be drawn, and any hydrogen atoms attached to a heteroatom must also be drawn. For example ... 

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... 

Substances that contain one or more atoms other than carbon as part of a nng are called heterocyclic compounds Rings m which the heteroatom IS oxygen nitrogen or sulfur rank as both the most common and the most important... 

Major unknowns in the mechanism by which a hydrocarbon fuel bums concern the pyrosynthesis reactions that lead to the formation of polycyclic aromatic hydrocarbons (PAHs) and soot and the oxidation chemistry of atoms other than carbon and hydrogen (heteroatoms) in the fuel, particularly nitrogen, sulfur, and halogens. 

Hess s law phys chem The law that the evolved or absorbed heat in a chemical reaction is the same whether the reaction takes one step or several steps. Also known as the law of constant heat summation. hes-oz, 16 hetero- chem Prefix meaning different for example, a heterocyclic compound is one in which the ring is made of more than one kind of atom. hed-o-ro heteroatom org chem in an organic compound, any atom other than carbon or hydrogen. hed-3-ro,ad-3m ... 

Cleavage (the breaking of a bond) next to a heteroatom (any atom other than carbon or hydrogen) is also relatively common. This is pcirticularly important if fragmentation involves the loss of a very stable molecule such as H2O or CO2 since this would indicate the presences of very pcirticular functional groups and thus would give clues to the structure of the molecule. 

Hetero-Diels-Alder products (i.e., Diels-Alder products involving an atom other than carbon) have also been observed for a number of systems at the Si(100)-2 x 1 surface. Some examples include the reaction of unsaturated ketones RC=C—CR=0 (e.g., ethylvinylketone) [255], 2-propenenitrile [256-260], and dicarbonyls 0=C—R—C=0 [261]. For a review specifically of heteroatom chemistry at the silicon surface, the reader is referred to Ref. [262]. Here we use the dicarbonyl example to provide an illustration of this class of surface chemistry. Hamers and coworkers have used the [4 + 2] heteroatom cycloaddition reaction of... 

Heteroatom Any atom other than carbon or hydrogen in an organic molecule. 

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). 

Theoreticians call any non-hydrogen atom a heavy atom, and any heavy atom other than carbon a heteroatom. In the Hiickel model, all carbon atoms are assumed to be the same. Consequently, their Coulomb and resonance integrals never change from a and If respectively. However, heteroatom X and carbon have different electronegativities, so we have to set ccx = a. Equally, the C-X and C-C bond strengths are different, so that Pcx X p. Thus, for heteroatoms, we employ the modified parameters... 

Any ring system containing at least one heteroatom (i.e. an atom other than carbon - typically nitrogen, oxygen, or sulphur) can be described as heterocyclic. This broad definition encompasses both aromatic heterocycles (such as pyridine 5.1) and their non-aromatic counterparts (piperidine 1.7). 

The key to chemical reactions, including terran biochemical reactions, at standard temperatures and pressures is the reactivity of carbon-carbon and carbon-hydrogen bonds in molecules that also contain carbon-heteroatom (any atom other than carbon or hydrogen) bonds. Bonds to heteroatoms are often said to activate carbon-carbon and carbon-hydrogen bonds. In terran metabolism, the most important heteroatoms are oxygen and nitrogen, although sulfur is also important, and other heteroatoms such as phosphorus occasionally play a role. 

Heteroatoms (hetero, different ) are any atoms other than carbon and hydrogen. The rule for calculating elements of unsaturation in hydrocarbons can be extended to include heteroatoms. Let s consider how the addition of a heteroatom affects the number of hydrogen atoms in the formula. 

Aromatic compounds are unsaturated cyclic molecules that possess additional stability as a result of the arrangement of 7i-electrons associated with the unsaturation of the ring system. This book will concentrate on the chemistry of benzene (4) and its derivatives and related polynuclear hydrocarbons. Aromatic compounds are also known as arenes they can becarbocydic, indicating that the ring skeleton contains only carbon atoms, or heterocyclic, with at least one atom other than carbon in the ring. These heteroatoms are typically N, O or S. Heterocyclic compounds, which can be aromatic or alicyclic, are covered in another book in this series. 

The term "heteroatom" applies to any atom other than carbon or hydrogen. It is common for heteroatoms to appear in locations that are inconvenient to name following basic rules, so a simple system called "replacement nomenclature" has been devised. The fundamental principle is to name a compound as if it contained only carbons in the skeleton, plus any functional groups or substituents, and then indicate which carbons are "replaced" by heteroatoms. The prefixes used to indicate these substitions are listed here in decreasing priority and listed in this order in the name ... 

A compound 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. A ring atom that is not carbon is called a heteroatom. The name comes from the Greek word heteros, which means different. The most common heteroatoms found in heterocyclic compounds are N, O, andS. 

Some amines are heterocyclic compounds—cyclic compounds in which one or more of the atoms of the ring is an atom other than carbon. Heterocyclic rings are numbered so that the heteroatom has the lowest possible number. A natural product is a compound synthesized by a plant or an animal. Alkaloids are natural products containing one or more nitrogen heteroatoms and are found in the leaves, bark, roots, or seeds of plants. 

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