Cycloalkanes defined

Waxes are less well defined aliphatic mixtures of n-alkanes, isoalkanes and cycloalkanes in various proportions. Their average molecular weights are higher than those of the paraffins from 600 to 800. 

A single alkane may have several different names a name may be a common name or it may be a systematic name developed by a well defined set of rules The most widely used system is lUPAC nomencla ture Table 2 6 summarizes the rules for alkanes and cycloalkanes Table 2 7 gives the rules for naming alkyl groups... 

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

In this section we consider the energetics of molecules with the generic formula cis- or (Z)-cyclo-[(CH2) -2 (CH=CH)] (1). A natural comparison of the enthalpies of formation of these olefins is with their saturated analogs, the cycloalkanes, with the generic formula, cyclo-[(CH2) -2 (CH2CH2)] [i.e. (CFL), 2], Using equation 13, let us now define the difference quantity < 13 (n) as the difference of the gas-phase enthalpies of formation of the cycloalkene of interest and the related cycloalkane ... 

We start with the unsubstituted cycloalkanones (38), compounds of the generic formula cyclo-[(CH2 ) -1 CO]. The gas-phase enthalpies of formation of all of these species from n = 3 to 12, 15 and 17 are available from experiment. An obvious comparison is with the corresponding n-membered ring cycloalkanes, cyclo-[(CH2)n]. Consider equation 38 in which the difference quantity 83% n) is defined as the difference of the gas-phase enthalpies of formation of the ketone of interest and the related cycloalkane. 

No, we will not attempt to discuss these halogenated cycloalkanes in the current chapter. Rather, we will discuss comparatively well-defined, and therefore relatively conceptually simple, species which gained prominence in our efforts simply because the desired thermochemical data are available. The initial post-introduction and technical section of this chapter relates to the energetics of mono-and di-halogenated derivatives of... 

FIGURE 4. Basis orbitals for (planar) cycloalkanes with ring size n. Basis orbitals comprise the radially oriented spi and spo hybrid orbitals at C, the tangentially oriented Pip (in plane) and Pop (out of plane) orbitals at C as well as in-phase and out-ofphase combinations of the two 1 s(H) orbitals, which combine with spo t and pop orbitals, respectively. Note that ethene is included as a two-membered ring where the ring is symbolized by two bent bonds and the CH bonds are shown to define the orientation of the ring plane (parallel to the drawing plane). The nature of each orbital set (c or n,... 

Define or identify each of the following terms (a) organic chemistry, (b) total bond order, (c) condensed formula, (d) structural formula, (e) fine formula, (/) hydrocarbon, (g) alkane, (h) aUcene, (/) alkyne, j) aromatic hydrocarbon, (k) saturated, (1) delocalized double bond, (m) isomerism, (n) cycloalkane, (o) radical, (p) functional group, (q) alcohol, (r) ether, (s) aldehyde, (f) ketone, (u) carbonyl group, and (v) ester. 

In examining the cycloalkenes, one must first recognize that a double bond has considerable inherent strain. For example, the dimerization of ethylene to give cyclobutane is fairly exothermic (—18 kcal mol" ) and if there were a way to readily overcome orbital symmetry restrictions, cyclobutane would be a very common reagent. However, in the following, we will take the conventional view that ethylene is unstrained. Then, in comparing cycloalkanes and cycloalkenes it is helpful to define olefinic strain (OS) as the difference in strain between the alkene and the corresponding alkane ... 

In contrast to the rotational freedom around single bonds in open-chain alkanes, there is much less freedom in cycloalkanes. Cyclopropane, for example, must be a rigid, planar molecule (three points define a plane). No bond rotation can take place around a cyclopropane carbon-carbon bond without breaking open the ring (Figure 3.8, p. 100). 

Contrary to what Baeyer predicted, cyclohexane is more stable than cyclopentane. Furthermore, cyclic compounds do not become less and less stable as the number of sides increases. The mistake Baeyer made was to assume that all cyclic molecules are planar. Because three points define a plane, the carbons of cyclopropane must lie in a plane. The other cycloalkanes, however, are not planar. Cyclic compounds twist and bend in order to attain a structure that minimizes Ae three different kinds of strain that can destabilize a cyclic compound ... 

Geometrical shapes such as the pentagon above are often used to show the structure of a cycloalkane. Recall that the intersection of two lines defines a carbon atom. 

The toxicokinetic properties of Stoddard solvent are not well defined by the available data. Some toxicokinetic data that are specific to the three classes of Stoddard solvent components (i.e., alkanes, cycloalkanes, and aromatics) are available. 

An exception is the halogenation of an alkane (or cycloalkane) whose hydrogen atoms are all equivalent (i.e., homotopic). [Homotopic hydrogen atoms are defined as those that on replacement by some other group (e.g., chlorine) yield the same compound (Section 9.8).]... 

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