Aromatic hydrocarbon One of a special

Aromatic hydrocarbon one of a special class of cyclic unsaturated hydrocarbons, the simplest of which is benzene. (22.3) Arrhenius concept a concept postulating that acids produce hydrogen ions in aqueous solution, whereas bases produce hydroxide ions. (7.1)... 

Aromatic hydrocarbon one of a special class of cyclic unsaturated hydrocarbons, the simplest of which is benzene. 

In recent years it has become clear that the structure of metals and alloys may be described in terms of covalent bonds that resonate among the alternative interatomic positions in the metals, and that this resonance is of greater importance for metals than for substances of any Other class, including the aromatic hydrocarbons. Moreover, the phenomenon of metallic resonance of the valency bonds must be given explicit consideration in the discussion of metallic valency it is necessary in deducing the metallic valency from the number of available electrons and bond orbitals to assign to one orbital a special r le in the metallic resonance. 

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

A class of hydrocarbons whose molecules contain a ring of six carbon atoms, each with only one hydrogen atom (or other group) attached, has special properties. The class is known as the aromatic hydrocarbons. The simplest member is benzene, and all other members have at least one benzene ring included... 

Another uniformity concerns the special stability of aromatic hydrocarbons having 4n + 2 tt electrons n = 1 for benzene, n = 2 for naphthalene, etc. The reeison lies in the observation that, in such cases, all bonding m.o.s are filled whereas the anti-bonding ones are vacant. In these hydrocarbons, except for the lowest energy tt m.o. (two electrons), the bonding tt m.o.s invariably occur in pairs of degenerate orbitals - 4n electrons hence a total number of 4 -I- 2 bonding electrons. 

Hydrocarbons are composed only of carbon and hydrogen and fall into two major classes - saturated and unsaturated. Saturated hydrocarbons or the alkanes are entirely constructed of single bonds and have the general formula CnH2n+2- Unsaturated hydrocarbons include the alkenes (CnH2n) in which there is at least one carbon-carbon double bond the alkynes (CnH2n-2) where there is at least one carbon-carbon triple bond and aromatic hydrocarbons which appear to have double bonds but actually have a special structure that is discussed in Chapter 6. 

A special case is the dehydrocyclization of paraffins—a complicated reaction similar to the previous one. Aromatic hydrocarbons are formed in it by way of dehydrogenation of the intermediate six-membered rings... 

Aromaticity is a cornerstone of chemistry, accounting for more than three quarters of aU known and recorded substances (about 60 million). It was discussed recently in Chemical Reviews a special issue published in 2001 reviewed most of the recent developments in aromaticity (Schleyer 2001) other relevant reviews have been published soon afterwards one on polycyclic aromatic hydrocarbons... 

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