Saturated, Cyclic Hydrocarbons

Group VI. Concentrated sulphuric acid provides a simple test for the diflferentiation inter alia between (a) saturated paraffin and cyclic hydrocarbons and also simple aromatic hydrocarbons and (b) unsaturated hydrocarbons. 

Saturated cyclic hydrocarbons, normally known as naphthenes, are also part of the hydrocarbon constituents of crude oils. Their ratio, however, depends on the crude type. The lower members of naphthenes are cyclopentane, cyclohexane, and their mono-substituted compounds. They are normally present in the light and the heavy naphtha fractions. Cyclohexanes, substituted cyclopentanes, and substituted cyclohexanes are important precursors for aromatic hydrocarbons. 

We JI look in the next chapter at cycloalkanes—saturated cyclic hydrocarbons— and we ll see that the molecules generally adopt puckered, nonplanar conformations. Cyclohexane, for instance, has a puckered shape like a lounge chair rather than a flat shape. Why ... 

Saturated cyclic hydrocarbons are called cycloalkanes, or alicyclic compounds (aliphatic cyclic). Because cycloalkanes consist of rings of -CH2- units, they have the general formula (CH2) , or and can be represented by polygons... 

A cycloalkane is a saturated cyclic hydrocarbon with the general formula C H2 . In contrast to open-chain alkanes, where nearly free rotation occurs around C, -C bonds, rotation is greatly reduced in cycloalkanes. Disubstituted cycloalkanes can therefore exist as cis-trans isomers. The cis isomer has both substituents on the same face of the ring the trans isomer has substituents on opposite faces. Cis-trans isomers are just one kind of stereoisomers—isomers... 

Alcohol derivatives of saturated cyclic hydrocarbons Steroid alcohols (e.g., cholesterol)... 

Similar calculations for saturated cyclic hydrocarbons show that a three- ... 

Thus, all five triple bonds in decamethyl[5]pericycline 3 can be completely hydrogenated to yield the corresponding saturated cyclic hydrocarbon 78 under platinum catalysis (Pt02, Adam s catalyst), albeit with some difficulty (Fig. 6). 

The nature of dangerous reactions involving organic chemicals depends on the saturated, unsaturated or aromatic structures of a particular compound. Saturated hydrocarbons are hardly reactive, especially when they are linear. Branched or cyclic hydrocarbons (especially polycyclic condensed ones) are more reactive, in particular as with oxidation reactions. With ethylenic or acetylenic unsaturated compounds, the products are endothermic . 

The chromatograms of the liquid phase show the presence of smaller and larger hydrocarbons than the parent one. Nevertheless, the main products are n-alkanes and 1-alkenes with a carbon number between 3 to 9 and an equimolar distribution is obtained. The product distribution can be explained by the F-S-S mechanism. Between the peaks of these hydrocarbons, it is possible to observe numerous smaller peaks. They have been identified by mass spectrometry as X-alkenes, dienes and also cyclic compounds (saturated, partially saturated and aromatic). These secondary products start to appear at 400 °C. Of course, their quantities increase at 425 °C. As these hydrocarbons are not seen for the lower temperature, it is possible to imagine that they are secondary reaction products. The analysis of the gaseous phase shows the presence of hydrogen, light alkanes and 1-alkenes. 

The simplest of the saturated cyclic hydrocarbons, or cycloalkanes, is cyclopropane, C3Hg, the molecules of which are made up of three carbon atoms to each of which two hydrogen atoms are attached. Cyclopropane is somewhat more reactive than the corresponding open-chain alkane, propane, C3Hg. Other cycloalkanes make up a part of ordinary gasoline. 

In saturated cyclic hydrocarbons, diamagnetic currents are induced due to circulating bond electrons. Although, the effect is weak, but this is sufficient to distinguish between axial and equatorial protons is cyclohexane. The axial protons are shielded and they absorb 0.5 ppm upfield as compared to the equatorial. 

Codec, H.D.K. Excited States of a Number of Saturated and Cyclic Hydrocarbons due to Irradiation. INIS-mf-5335, 7.Jun.l979. 

Bivalent radicals derived from saturated or unsaturated mono-cyclic hydrocarbons by removing a hydrogen atom from each of two different carbon atoms of the ring are named by replacing the endings... 

Chart 4. Structural Relation of Monocyclic Terpene Hydrocarbons to Aromatic and Saturated Cyclic Hydrocarbons... 

Another means of classification depends on the type of bonding that exists between carbons. Hydrocarbons which contain only carbon-to-carbon single bonds are called alkanes. These are also referred to as saturated molecules. Hydrocarbons containing at least one carbon-to-carbon double bond are called alkenes, and those compounds with at least one carbon-to-carbon triple bond are called alkynes. These are compounds that are referred to as unsaturated molecules. Finally, a class of cyclic hydrocarbons that contain a closed loop (sextet) of electrons are called aromatic (see Chapter 14 in your text for further details). Table 28.1 distinguishes between the families of hydrocarbons. 

All monochlorinated saturated cyclic hydrocarbons from propane to hexane have been studied in the gas phase. The data in Table 25 demonstrate a definite correlation between the ring size and the C—Cl bond distances. The exocyclic bonds lengthen steadily from 174.0(11) pm in the three-membered ring to 181.0(4) pm in the five-membered ring and... 

The cyclic hydrocarbons, such as cyclohexane, act much in the same manner as the aliphatic hydrocarbons. A significant percentage of quantity inhaled may be metabolized to compounds with a lower order of toxicity. The unsaturated cyclic hydrocarbons generally are more irritating than the saturated forms. 

Multimetallic sandwiches, including polymetallocenes, bis(fulvalene)-dimetal compounds, multi-decker sandwiches, and compounds in which two metals are bonded to a common unsaturated cyclic hydrocarbon are discussed in Section II. Sections III and IV are subdivided according to the metal group, and describe ligand-bridged bimetallics and metal clusters, respectively. Where appropriate, redox potentials have been included. Unless otherwise stated they are referenced versus the aqueous saturated calomel electrode (see). 

The octane number of the gasoline fraction composed of the aliphatic polyester fragments could be predicted by taking into account the linear and cyclic oxygenated saturated hydrocarbon nature of the components. 

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