Odd-numbered hydrocarbons

Within the VGO saturates, distribution of paraffins, isoparaffins, and naphthenes is highly dependent on the petroleum source. The naphthenes account for roughly 60% of the saturates in a normal cmde oil. However, samples can be found having paraffins from <20 to >80%. In most samples, the / -paraffins from C2Q—are still present in sufficient quantity to be detected as distinct peaks in gc analyses. Some cmde oils show a nearly symmetric pattern of peaks such that each carbon number is present in regular progression up to a maximum around C -j. Other cmde oils show a similar distribution, but have preference for odd-numbered alkanes. Both the distribution and the selectivity toward odd-numbered hydrocarbons are considered to reflect differences in petrogenesis of the cmde oils. Although / -paraffins are distinct in the gc, these usually account for only a few percent of the saturates measured by gc. 

The CPI25-35 for plant wax n-alkanes is in the range of 5-10, meaning on average that each odd-numbered hydrocarbon is 5-10 times more abundant than the even-numbered molecules with one more or one... 

Strong evidence for the biogenesis of kerogen was shown when it was found that the ratio of odd to even number of carbon atoms in the extracted hydrocarbons was as high as four to one. A ratio of one to one would be expected from a nonbiological source. The higher proportion of the odd number hydrocarbons would be anticipated if their source was the decarboxylation of algal fatty acids, since these acids are predominantly even number acids. 

Hydrocarbons are compounds containing only hydrogen and carbon. Plants manufacture hydrocarbons as components of the membranes of cells and vesicles. The biosynthetic pathway leads mainly to compounds with an odd number of carbon atoms. Figure 1-3 shows the concentrations of hydrocarbons washed from the air by rain in the winter and summer. The preponderance of odd-number hydrocarbons in the summer suggests that the source is mainly from plants. The more uniform distribution of odd- and even-number hydrocarbons in the winter suggests a manmade origin. The concentration of C29H60 in summer rainwater is 34 ppb. Find the molarity of this compound in nanomoles per liter (nM). 

Aliphatic hydrocarbons can be prepared by the reduction of the readily accessible ketones with amalgamated zinc and concentrated hydrochloric acid (Clemmensen method of reduction). This procedure is particularly valuable for the prep>aration of hydrocarbons wdth an odd number of carbon atoms where the Wurtz reaction cannot be applied with the higher hydrocarbons some secondary alcohol is produced, which must be removed by repeated distillation from sodium. 

Some species have an odd number of valence electrons, and so at least one of their atoms cannot have an octet. Species having electrons with unpaired spins are called radicals. They are generally highly reactive. One example is the methyl radical, CH, which is so reactive that it cannot be stored. It occurs in the flames of burning hydrocarbon fuels. The single unpaired electron is indicated by the dot on the C atom in -CHj. 

One final note on this topic involves an examination of diploid, triploid, and tetraploid plants for their leaf exudate hydrocarbons (Seigler et al., 1975). -Alkanes having odd numbered chains from to were recorded for almost all plants collected from several sites with much more limited distribution of hydrocarbons based on and C g. The hydrocarbon data do not assist in distinguishing groups within this species. 

Most moth sex pheromones that are straight chain hydrocarbons also usually have an odd number of carbons. Most of these are polyunsaturated with double bonds in the 3,6,9- or 6,9-positions, indicating that they are derived from linolenic or linoleic acid, respectively [49,51]. Iinolenic and linoleic acid cannot be biosynthesized by moths so they must be obtained from the diet [75]. A few even chain-length hydrocarbon sex pheromones have been identified that also have 3,6,9- or 6,9-double bond configurations [49], indicating they too are derived from linolenic or linoleic acids however, it is not known how these even chain hydrocarbons are formed. 

Adjacent polyenes are hydrocarbons with double bonds between each pair of atoms in the polyene system they are called cumulenes2. Two types of cumulenes exist those with an even number of adjacent double bonds and those with an odd number. The former can exhibit chirality, the latter geometric isomerism. Allenes (propadienes) are the simplest members of the even-numbered type of cumulenes. 

It is likely that the spectrum of compounds produced by all Mastophora species includes a wider range of compounds than those found in this study. Several Mastophora species catch male moths that are known to respond to pheromone compounds in the even-carbon number aldehyde/ acetate/alcohol chemical class, as well as males of other species that are known to respond to pheromone compounds in the odd-carbon number hydrocarbon chemical class (9, 13). 

When a proton addition complex is formed, the particular even-numbered hydrocarbon is converted to an odd hydrocarbon ion. The TT-electron number remains even, but is reduced by two as a result of the formation of the u-bond. Thus we are dealing with a diamagnetic positive hydrocarbon ion. The theoretical treatment of this 7r-electron system has to reflect the following ... 

Note 5 A liquid-crystal dimer with flexible hydrocarbon chains having an odd number of carbon atoms is called an odd-membered liquid-crystal dimer, whilst one with hydrocarbon chains having an even number of carbon atoms is called an even-membered liquid-crystal dimer. 

Aliphatic Nitro Compounds The molecular ion peak (odd number) of an aliphatic mononitro compound is weak or absent (except in the lower homologs). The main peaks are attributable to the hydrocarbon fragments up to M — N02. Presence of a nitro group is indicated by an appreciable peak at m/z 30 (NO+) and a smaller peak at mass 46 (N02+). 

The molecular ion peak (odd number) of aliphatic nitrites (one N present) is weak or absent. The peak at m/z 30 (NO+) is always large and is often the base peak. There is a large peak at m/z 60 (CH2=ONO) in all nitrites unbranched at the a carbon this represents cleavage of the C—C bond next to the ONO group. An a branch can be identified by a peak at m/z 74, 88, or 102,. Absence of a large peak at m/z 46 permits differentiation from nitro compounds. Hydrocarbon peaks are prominent, and their distribution and intensities describe the arrangement of the carbon chain. 

Normal alkanes are hydrocarbons with the formula C H2 +2. Plants selectively synthesize alkanes with an odd number of carbon atoms. The concentration of C29HM) in summer rainwater collected in Hannover, Germany, is 34 ppb. Find the molarity of C29HW) and express the answer with a prefix from Table 1-3. 

About 11% were unsaturated hydrocarbons ranging from Ci4 to C-29. The main components were the odd-numbered, saturated hydrocarbons with carbon numbers 23, 25, and 27. The even-numbered hydrocarbons are found in lesser amounts and have a maximum at C24 (12) (Table III). 

Since carbon-halogen bond cleavage is not a favorable process, and since both carbon and oxygen atoms have an even number of electrons, the oxidation proceeds either via free radicals or via carbenes and triplets. As a result, the oxidation mechanisms are considerably simpler than with hydrocarbons. Section III of this review treats free radical oxidation, whereas Section IV treats oxidation by processes not involving free radicals. In this discussion a free radical is considered to be a species with an odd number of electrons carbenes and triplets are called biradicals and are not included in this category. 

Previous studies on heavy hydrocarbon content of young sediments showed that they contained all the n-paraffin series, but that those containing paraffins with odd numbers of carbon atoms were several times as abundant as those containing even numbers of carbon atoms. Bray and Evans (7) defined a ratio of odd to even paraffins as a carbon preference index (CPI). In Recent sediments (mostly from nearshore environments) the CPI varied from 2.5 to 5.5. Crude oils and extracts from ancient shales exhibited little odd-carbon preference. The CPI for ancient shales varied from 0.9 to 2.3 and that for crude oils from 0.6 to 2.2... 

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