Homologous series, carbon-number distribution

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. 

Table V illustrates the carbon-number distribution in selected series. Similar trends were observed in most others. With one exception, the homolog present in the largest concentration within a series has three to four carbon atoms more than the first member of the series. This could indicate short sidechains or, possibly, the appearance of isomeric naphthenoaromatic series...

Table V. Carbon-Number Distribution in Selected Homologous Series in EDS Asphaltenes...

The overall distribution of the components determined is shown in Table II. Items reported for each class of components include total amount, the number of homologous series (in Z number), and individual carbon-number homologs determined in that class and their ranges (in carbon number). 

Distribution constants of homologous series of compounds can be reconstructed empirically by the group distribution constants. For example, the distribution constants of keto and enol forms of n-alkyl substituted (3-diketones in CCI4/H2O were linearly increased with the carbon numbers of the n-alkyl substituent as shown in Figure 2.3. The increment of 0.64 refers to the distribution constant of -CH2- [2]. 

---