Carbon ring structures

Steroids are the only common lipids without fatty acids. Chemically, they consist of a fused carbon ring structure consisting of four rings, three rings of which are six membered and one ring of which is five membered, as shown in Figure 16.5. Some steroids, such as cortisone, function as hormones. Cholesterol is an important component of membranes in animal cells. 

The monocyclic terpene hydrocarbons, many of which are formed readily from the acyclic terpenes by ring closure or from the bicyclic terpenes by ring fission, contain a six-carbon ring and may all be considered as derivatives of either cyclohexane or benzene. They may also be classified, on the basis of common larger fundamental structures, into two distinct types of substituted six-carbon ring structures ... 

Lactone An organic compound that contains an ester group incorporated into a carbon ring structure. Lactones include the coumarins, e.g. umbelliferone or 7-hydroxycoumarin. Lactones and furocoumarins, e.g. bergaptene, exist in small quantities in essential oils and should be used with care. Lactones can be neurotoxic (poisonous to the nervous system) and cause skin allergies. Bergaptene is well known for its phototoxicity on the skin. 

Cyclo-olefins are subject to structural isomerization in contact with acidic catalysts, as Bloch and Thomas (27) and Greensfelder and Voge (21) have shown. Therefore, such catalytic activity when intimately coupled to the aromatization reaction may direct the reaction path to products having five-carbon ring structures which cannot aromatize ... 

In addition to aromatics with benzene ring structures, modern refinery processes tend to increase the number of hydrocarbons with simpler types of carbon ring structures. Typical chemicals include cyclopentane, where the straight-chain pentane has been wrapped into a five-carbon ring. Other transformations of aliphatic hydrocarbons include cylcohexane and cyclopentane. These ring compounds are usually called naphthenes. 

Derivation (Natural) Secretion from preputial follicles of the musk deer. Synthetic (1) Ketones and lactones with 15- or 16-carbon rings, structurally resembling the odoriferous principles of natural musk, civet, and musky-type plants. Among these are ambrettolide, civetone, muscone, exaltolide. (2) Nitrated compounds, usually nitrated ferf-butyl-tol-uenes or xylenes or related compounds. The three most commonly used in perfumery are musk am-brette, musk ketone, and musk xylene. 

The phenomenon of changing of carbon ring structures by means of carbon shifts, is known as the Wagner-Meerwein rearrangement, after its discoverers. 

Steroids are a class of lipids that have a characteristic carbon ring structure of the t5rpe... 

A good example of this is a complex assembly of proteins called Complex III (Figure 5.3). This is one of four protein complexes that moves electrons to oxygen, all of which contain electron-paths made of iron, sulfur, and carbon rings (plus a few coppers at the end). Complex III has 12 structures that can hold electrons two iron-sulfur chunks, six irons surrounded by a heme belt hke in hemoglobin, and four carbon ring structures. (That s a lot of iron.) These are arranged in two paths of six structures each, so that the electrons hop from one to the next in a defined order like a bus on its route. 

Aromatic Hydrocarbons Aromatic hydrocarbons are characterized by one or more six-carbon ring structures with one hydrogen atom per carbon atom. The name aromatic comes from the solvent s aroma. On the whole, aromatic hydrocarbons are local irritants and vasodilators that cause severe pulmonary and vascular injury when absorbed into the body in sufficient concentrations. They can cause dermatitis and can be potent narcotics, with effects on the central nervous system. Of this group, benzene—with its link to leukemia—is strongly regulated and appears to be the most toxic aromatic hydrocarbon. Examples of aromatic hydrocarbons and their respective TLVs are benzene (0.5 ppm), toluene (50 ppm), and xylene (100 ppm). 

Carbon ring structures are common in organic chemistry. Draw a Lewis structure for each carbon ring structure, including any necessary resonance structures. 

The incorporation of tritium only into the streptidine moiety suggested a direct incorporation of the intact cyclitol without fission of the carbon ring structure. The fact that the intracellular contents were essentially devoid of tritiated water supported this finding. 

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