Homologous series, carbon-number

Formula Class Relative Mole Percent of Those Compounds That Ionized Number of Homologous Series Z Number Range Number of Individual Homologs Observed Carbon Number Range... 

The weight percents of the individual homologs in each specific-Z series (carbon-number distributions) were calculated from LV/EI/MS molecular-ion intensities assuming constant mole sensitivities for each specific-Z series. An invalid factor was inadvertently used in the previous conversion of the LV/EI/MS carbon-number distributions for the asphaltene neutral fraction to carbon-number distributions based on the total liquid. Consequently, the entries in the LV/EI/MS carbon-number distributions for Z(H), Z(O), and Z(S) asphaltene neutral aromatic compounds in References 35 and 47, the total weight percentages of these specific-Z series in References 35, 47, and 48, and the sums of these latter weight percentages reported in all these references should be multiplied by 0.892. 

If the departure from equation (35) is not too large, it can be treated as a perturbation. The effect of non-central interactions on the second virial coefficient is second order and it is very difficult to distinguish between any of the non-central interactions on the basis of the behaviour of In essence, it is possible to fit the properties of many pure substances to equations based on simple corresponding states and additional terms whose magnitude is proportional to a perturbation parameter that is a measure of the deviation from central forces. One such perturbation parameter is Pitzer s acentric factor. 74,76 another is Rowlinson s In a homologous series the number of carbon atoms in the chain constitutes yet another measure of the perturbation. It can be shown that there is a simple relation between the different factors. ... 

Later, an exhaustive study of 17 genus of the subfamily Aroideae of Araceae revealed the presence of three major acids, 11-phenylundecanoic acid, 13-phenyltridecanoic acid and 15-phenylpentadecanoic acid in seed lipids. Other odd carbon number acids from C7 to C23 were detected but in trace amounts. Similarly, two series of homologous odd carbon number monounsaturated w-phenylalkanoic acids were found. Thus, it can be stated that all odd carbon chain w-phenylalkanoic acids from Cl through C23 have been found in nature. Furthermore, even carbon chain w-phenylalkanoic acids from CIO through C16 were also detected. 

On nonpolar columns, the compounds of a homologous series separate as a function of their boiling points, and linear relationships have been established between the logarithms of the retention volumes and the number of carbon atoms in the 2-, 4-, and 5-positions (see Fig. III-l). 

Formic acid [64-18-6] (methanoic acid) is the first member of the homologous series of alkyl carboxyHc acids. It occurs naturally ia the defensive secretions of a number of insects, particularly of ants. Although the acid nature of the vapors above ants nests had been known since at least 1488, the pure acid was not isolated until 1671, when the British chemist John Ray described the isolation of the pure acid by distillation of ants (1). This remained the main preparative method for more than a century until a convenient laboratory method was discovered by Gay-Lussac (2). The preparation of formates using carbon monoxide was described by Berthelot in 1856. 

Naphthenic acids are lepiesented by a general formula where n indicates the carbon number and specifies a homologous series. The ... 

Another method of estimating autoignition temperatures is to compare values for a compound with other members of its homologous series on a plot vs. carbon number as the temperature decreases and carbon number increases. Affens gives a formal procedure for such estimation. 

Development of the Nomograph. Tw o main sources of data were used to develop the nomograph McAuliffe and Price. The hydrocarbons were divided into 14 homologous series as listed in Table 1. Solubilities at 25°C were then regressed with the carbon numbers of the hydrocarbons in order to obtain the best fit for each homologous series. A second order polynomial equation fits the data very well ... 

Table 2.3 lists the heats of combustion of several alkanes. Unbranched alkanes have slightly higher heats of combustion than their 2-methyl-branched isomers, but the most important factor is the number of carbons. The unbranched alkanes and the 2-methyl-branched alkanes constitute two separate homologous series (see Section 2.9) in which there is a regular- increase of about 653 kJ/mol (156 kcal/mol) in the heat of combustion for each additional CH2 group. 

Alkenes also form a homologous series as the carbon number increases, the number of possible isomeric structures for each member increases more rapidly than in the case of the alkane series. 

The Krafft temperature for a homologous series rises as the chain length increases but with independent and different curves for even or odd members [80]. Figure 7 shows the Krafft temperatures of sodium alcohol sulfates ranging from 11 to 18 carbon atoms where the two different curves for odd- and even-numbered series and the alternancy of values can be clearly observed. Lange and Schwuger explain this effect as caused by the different crystal structures of the even and odd numbers. 

Sodium a-sulfonated fatty acid esters of long-chain alcohols have a structural effect on the Krafft point different from that of amphiphiles with short alkyl chains [60]. In a series of homologs with the same total carbon number the Krafft points are highest when the hydrophilic alkyl chain lengths in the a-sulfonated fatty acid and the alcohol are fairly long and equal. In this case the packing of the molecules becomes close and tight. 

Mathematical methods for determining the gas holdup tine are based on the linearity of the plot of adjusted retention time against carbon number for a homologous series of compounds. Large errors in this case can arise from the anomalous behavior of early members of the homologous series (deviation from linearity in the above relationship). The accuracy with which the gas holdup time is determined by using only well retained members of a homologous series can be compromised by instability in the column temperature and carrier gas flow rate [353,357]. The most accurate estimates... 

Waggott [57] reported that a factor of major concern in adapting the technique to more polluted samples is the capacity of the carbon filter, which usually contains only 1.5-2 mg carbon. He showed that the absolute capacity of such a filter for a homologous series of 1-chloro-n-alkanes was 6 xg for complete recovery. Maximum recovery was dependent on carbon number, being at a maximum between Cs and C12 for the 1-chloro-n-alkane series. It is important, therefore, to balance the amount of sample stripped with the capacity of the carbon filter to obtain better than 90% recoveries. 

A classic method14 for examining the thermochemical regularity of an organic homologous series is plotting the standard molar enthalpies of formation versus the number of carbon atoms in the compounds. The linear relationship may be expressed as equation 1 where all the enthalpies of formation are in either the gaseous or a condensed phase, a is the slope, ft is the y-intercept and nc is the number of carbon atoms in the compound. 

Fig. 3 Deviations from linearity of the enthalpies of formation of several homologous series of hydrocarbons, expressed as the value of 5 in (28), and plotted against the number of carbon atoms m in the normal alkyl radical. (Reproduced with permission from Stull et al., 1969)...

The alkanes make up a homologous series of hydrocarbons with the general formula C H2 +2 in is the number of carbon atoms). Alkanes exhibit a type of structural isomerism called chain isomerism, where the arrangement of the carbon atoms in the molecules is different. 

If a sample contains one or more members of a homologous series, identifications can be made using a plot of log tR against the number of carbon atoms, previously prepared from standards. The plot, which is valid for one temperature only, is linear and can be used for alkanes, alkenes, alcohols, aldehydes, ketones, esters and ethers. 

A universal system for qualitative identification was devised by Kovats some years ago. Based on the linear relation between log t R and the number of carbon atoms for a homologous series, Kovats selected //-alkanes as standards for the following reasons ... 

The saturated open-chain hydrocarbons form a homologous series called the paraffin series or the alkane series. The composition of each of the members of the series corresponds to the formula CnH2n + 2> where n is the number of carbon atoms in the molecule. All the members of the series are unreactive. They do not react readily at ordinary temperatures with such reagents as acids, alkalies, or oxidizers. 

Since members of a homologous series have incremental boiling point differences and if the amount of any homolog in the moving gas phase is related to vapor pressure at the temperature of the experiment, plots of log k vs. carbon number should also be a straight line. (The enthalpy of vaporization increases monotonically with carbon number.) This in fact is observed in gas-liquid equilibrium separation systems. It is the basis of retention index systems pioneered by Kovats for qualitative identification. 

For higher members of a homologous series with approximately the same polarity, the logarithm of the capacity factor varies linearly with the molar volume or the carbon number. 

It has been firmly established that thermochemical properties of a homologous series of compounds show a linear dependence on the number of carbon atoms in the alkyl group1,9 11. Especially useful is equation 1 which expresses the standard molar enthalpies of formation of a homologous series as a function of the total number of carbon atoms in the compound, nc. 

Because the enthalpies of formation of a homologous series correlate with the number of carbon atoms according to equation 1, the enthalpies of formation of any one series must correlate with the enthalpies of formation of any other series with like nc, as in equation 2. 

Homologous long chain -alkane series ranging from C38 with no carbon number predominance [ 1,53 - 55,73,109 -114]... 

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