Polycyclic compounds cycloalkanes

One of the most ubiquitous multiple-component contaminants that reaches the soil and deeper subsurface layers is crude oil and its refined products. In the subsurface, these contaminants are transformed differently by various mechanisms (Cozzarelli and Baber 2003). Crude oil contains a multitude of chemical components, each with different physical and chemical properties. As discussed in Chapter 4, the main groups of compounds in crude oils are saturated hydrocarbons (such as normal and branched alkanes and cycloalkanes without double bonds), aromatic hydrocarbons, resins, and asphaltenes, which are high-molecular-weight polycyclic compounds containing nitrogen, sulfur, and oxygen. 

We also discuss the conformations of cycloalkanes, especially cyclohexane, in detail because of their importance to the chemistry of many kinds of naturally occurring organic compounds. Some attention also will be paid to polycyclic compounds, substances with more than one ring, and to cyclo-alkenes and cycloalkynes. 

Although Hantzsch-Widman system works satisfactorily (if you can remember the rules) for monocyclic compounds, it is cumbersome for polycyclic compounds. In the case of oxiranes it is simplest for conversational purposes to name them as oxides of the cycloalkenes or epoxy derivatives of the corresponding cycloalkanes. The oxabicycloalkane names seem preferable for indexing purposes, particularly because the word oxide is used in many other connections. 

The main groups of compounds in crude oils are saturated hydrocarbons (such as normal and branched alkanes and cycloalkanes that contain no double bonds), aromatic hydrocarbons, resins and asphaltenes (higher molecular weight polycyclic compounds containing nitrogen, sulfur. 

Some representative strained organic molecules in dijferent classes A) simple, spiro, and fused cycloalkanes B) distorted and twisted alkenes C) strained polycyclic compounds... 

Because these systematic names are so unwieldy, organic chemists often assign a name to a polycyclic compound that is more descriptive of its shape and structure. Dodecahedrane is named because its 12 five-membered rings resemble a dodecahedron. Figure 4.4 shows the names and structures of several other cycloalkanes whose names were inspired by the shape of their carbon skeletons. All the names end in the suffix -ane, indicating that they refer to alkanes. 

The final point we ll consider about cycloalkane stereochemistry is to see what happens when two or more cycloalkane rings are fused together along a common bond to construct a polycyclic compound—for example, decalin. 

Alicyclic Hydrocarbons. These refer to cyclic analogues of aliphatic hydrocarbons and are named accordingly, using the piefix cyclo-." Their properties are similar to their open-chain aliphatic counterparts. Alicyclic hydrocarbons are subdivided into monocyclic (cycloalkanes, cycloalkenes, cycloalkynes, cycloalkadienes, etc.) and polycyclic aliphatic compounds. Monocyclic aliphatic structures having more than 30 carbon atoms in the ring are known, but those containing 5 or 6 carbon atoms are more commonly found in nature [47, p. 28]. 

Among the multitude of organic compounds, there is a small number of objects with p 0 (all types of acyclic compounds most topologically relevant to n-alkanes). The increase in number of cycles in the molecules leads to the increase of p up to 0.3-0.5 (cycloalkanes, arenes, etc.), 0.5-0.8 (naphthalenes, biphenyl, etc.), and 1.0 and more retention index units per degree (i.u./deg) for tri- and polycyclic structures. Hence, it is not surprising that RI data for isoalkanes, ethers, esters, etc. being measured at different conditions, are in good accordance with each other (standard deviations of randomized interlaboratory values are not more than 1-3 i.u.). The same statistical characteristics for substituted benzenes is about 8 i.u., and for naphthalenes and other condensed arenes, it may exceed 10-15 i.u. 

Cycloalkanes are bonded in the same way as noncyclic alkane molecules— by overlap of s- hybrid orbitals. Ring compounds have sides, which means that substituents can be on the same side (cis) or on opposite sides (trans). All manner of polycyclic molecules (two or more rings) exist. 

The cycloalkanes discussed so far contain only one ring and therefore may be referred to as monocyclic alkanes. In more complex structures—the bi-, tri-, tetra-, and higher polycyclic hydrocarbons—two or more rings share carbon atoms. Many of these compounds exist in nature with various alkyl or functional groups attached. Let us look at some of the wide variety of possible structures. 

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