Homologous Series Cycloalkanes

Saturated, polycyclic (alicydic) hydrocarbons are composed of three tetracoordinate building blocks quaternary C , tertiary CH- and secondary -CH2-. As we address the question of homologies for these species, we must accept that there are idiosyncrasies arising from the varying sizes of the component 

For example, consider the series cydohexane 1, trans-decalin 2, and trans-syn-trans-perhydroanthracene 3 (CH2)e(CH)o, (CH2)8(CH)2, (CH2)io(CH)4 with their increasing numbers of secondary and tertiary carbons and 6-membered rings (6MR). The members of this series differ by a constant [(CH)2(CH2)2] structural unit. 

Since their respective enthalpies of formation (-123.4 0.8, -182.1 2.3 an i 243.2 3.8 kJ mol1) linearly correlate (r2 = 0.9999) with the number of such structural units, it follows that the reaction 

Another series of 6-membered ring speries is cydohexane, adamantane 4, diamantane 5 (CH)o(CH2)e, (CH)4(CH2)e, (CH)8(CH2)e with their increasing numbers of tertiary carbons and 6-membered rings. Note that this series is not homologous in the sense we have used previously, in that the [(CH)4] increase between members of the series occurs in a disconnected manner. 

Let us now consider tetrahedrane 6 and [l.l.l]propellane 7. Both species have numerous 3MRs or cyclopropane rings. We thus expect both compounds to be highly strained. Do these hydrocarbons belong to anv homologous series Are they to be understood as avatars for the study of yet more wondrous strained species Are they, as it were, alicycles resplendent in glorious isolation despite the considerable attention paid to both tetrahedrane [27] and [l.l.l]propellane [28] by computationally oriented theoretical chemists  

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Physical properties of cycloalkanes [49, p. 284 50, p. 31] show reasonably gradual changes, but unlike most homologous series, different members exhibit different degrees of chemical reactivity. For example, cyclohexane is the least reactive member in this family, whereas both cyclopropane and cyclobutane are more reactive than cyclopentane. Thus, hydrocarbons containing cyclopentane and cyclohexane rings are quite abundant in nature. 

Cycloalkanes are alkanes that are cyclic with the general formula C H2 . The simplest members of this class consist of a single, unsuhstituted carhon ring, and these form a homologous series similar to the unbranched alkanes. The C3 to Ce cycloalkanes with their structural representations are shown below. 

The product consists uf various amounts of high polymer (.r is very large) and discrete cyclosilanes with n = 5-35. This is the largest homologous series of cyclic compounds now known except for the cycloalkanes. Although these compounds are formally saturated, they behave in some ways as aromatic hydrocarbons. They can be reduced to amon ladicals. and EPR spectra indicate that the unpaired electron is delocalized over the entire ring. 06... 

Unlike most homologous series, the different members of the cycloalkane family exhibit different chemical reactivities. We already have seen that chemical reactivity is related to the strain in the carbon-carbon bonds and that ideally the carbon bonds should have bond angles of 109.5°. 

The relation between molecular size, Tl, and the relaxation mechanisms is apparent from the homologous series of cycloalkanes. 7, and NOE data as well as the contributions of the DD and SR mechanisms accessible from these experimental values via eqs. (3.20) and (3.21) are listed in Table 3.15. The I3C nuclei of cyclopropane relax almost as fast by spin-rotation as by the DD mechanism (7, (SR) Ti (DD)). However, in cyclobutane the DD mechanism predominates (7, (DD) < 7, (SR)), and the carbon atoms of cyclohexane and its higher homologs relax exclusively by the DD mechanism (71(DD 71(SR ) [160],... 

Solubility-Molar Volume Relationships The correlation between aqueous solubility at room temperature and the molar volume has been studied by McAuliffe [5] for different hydrocarbon classes. He discusses linear relationships, presented as graphs, describing the decrease in solubility with increasing molar volume for the homologous series of alkanes, alkenes, alkandienes, alkynes, and cycloalkanes. 

Know the meaning of saturated hydrocarbon, alkane, cycloalkane, homologous series, methylene group. 

Figure 6.5. Homologous series plots (a) linear (b) logarithmic. 1 = alkanes, 2 = cycloalkanes, 3 = esters, 4 = aldehydes, 5 = ketones, 6 = alcohols. Reprinted with permission from J. S. Lewis, H. W. Patton, and W. I. Kaye, Anal. Chem. 1956, 28, 1370. Copyright 1956, American Chemical Society.

Write the general formulas for the alkane, alkene, alkyne, and cycloalkane homologous series. 

The following could be documented with the homologous series of cycloalkanes ... 

As in the case of cycloalkanes, the types of motion in the homologous series of phenylenes is strongly size dependent. Figure 5.1 shows the thermal transition temperatures as a function of phenylene groups and in Table 5.1 the transition entropies are listed. The first member of the series shows no thermal transitions below the melting temperature (Sect. 5.1.1). With the second and third, a condis phase becomes obvious (Sect. 5.1.2) and with the fifth, liquid crystalline states exist in addition (Sect. 5.1.3). Poly-p-phenylene (Sect. 5.1.4) is the limiting member of these molecules. 

The fragmentation patterns of cycloalkanes may show mass clusters arranged in a homologous series, as in the alkanes. However, the most significant mode of cleavage of the cycloalkanes involves the loss of a molecule of ethene, either from the parent molecule or from intermediate radical-ions. The peak at mie = 42 in cyclopentane and the peak at mie = 56 in methylcyclopentane result from the loss of ethene from the parent molecule. Each of these fragment peaks is the most intense in the mass spectrum. 

The behavior of the substances specified in ASTM D 2887-84, Table X 1-1, (this Chapter, Table 3-2) is different because these substances are not members of an homologous series but represent olefins, cycloalkanes, aromatics, and heterocompounds. The condensed aromatics and the polar compounds containing heteroatoms such as oxygen, sulfur, or nitrogen diverge distinctly from the boiling behavior of the non-aromatics of equal molecular weight (Fig. 3-9). Therefore it is understood that the evaporation behavior in the thermobalance ist also different. 

FIGURE 37.1. Density as a function of repeat unit n for the homologous series of alkanes (o) and cycloalkanes (A). Reproduced from [1]. 

The pKj values of a homologous series (C - C ) of cyclopentyl and cyclohexyl carboxylic acids obtained at 298 K by titration have been reported and are just as expected. The proton ionization of cycloalkane-l,l-dicarboxylic acids in aqueous perchloric acid or sodium perchlorate solutions has also been studied. From the data obtained it is suggested that the solvent-solute interactions present can be related to the conformational features of the acids. 

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