Alkanes anteiso

FIGURE 9.47 Distribution of 2-niethyl (i iso) and 3-methyl (a anteiso) alkanes measured in (a) cigarette smoke, (b) particles from abrasion of leaves typical of the Los Angeles area, and (c) annual average concentrations measured in three locations in southern California in 1982 (adapted from Rogge et al., 1994). 

In addition, the /-C33 component is relatively more important in the leaf abrasion particles. Similarly, Kavouras et al. (1998) have shown that in addition to the concentrations and ratios of the iso- and anteiso-alkanes, there are other markers associated with the alkanes in cigarette smoke. For example, the CPI for cigarette smoke was measured to be 3.44 compared to 1.41-1.66 for particles in urban and suburban areas. (The CPI for rural areas was 4.53, reflecting the contribution from plant waxes.)... 

This paper presents data on isolation and identification of the following types of geolipids from the Aleksinac oil shale, a Miocene lake sediment n-al-kanes, iso- and/or anteiso-alkanes, aliphatic iso-prenoid alkanes, polycyclic isoprenoid alkanes, aromatic hydrocarbons, saturated unbranched, aliphatic isoprenoid, hopanoic, and aromatic mono- and poly-carboxylic acids, fatty acid methyl esters, aliphatic y- and 6-lactones, cyclic y-lactones, aliphatic methyl- and isoprenoid ketones, and the triterpenoid ketone adiantone. Possible origin of the identified compound classes is discussed, particularly of those which had not been identified previously as geolipids. 

Most of the geolipids so far identified in the oil shale from Aleksinac represent well known and ubiquitous constituents of sediments n-alkanes, iso- and anteiso-alkanes, aliphatic and cyclic isoprenoid alkanes including steranes, triterpanes and tetrater-panes, aromatic hydrocarbons, and aliphatic, hopanoic and aromatic acids. Moreover, several classes of compounds were identified which were also known as constituents of some ancient sediments but were not found to be ubiquitous, such as aliphatic isoprenoid ketones, aliphatic methyl ketones and the triterpenoid ketone adi-antone. 

Over 120 alkanes, ranging from the Cj hydrocarbon methane to the Cjg hydrocarbon hexatriacontane, have been identihed in tobacco and tobacco smoke. Many of the higher molecnlar weight alkanes have been reported to be present in three isomeric forms, that is, the normal, the iso (2-methyl-), and the anteiso (3-methyl-) isomer ... 

As listed in Table I.A-4, adapted from Mold et al. (2595), about 25% to 50% of the total alkanes in tobacco comprise nearly equal amounts of the iso and anteiso isomers of the alkanes. In the series of normal- and o-alkanes, the homologs with odd-numbered carbons predominate, with the C3, and C33 homologs being present in the largest amounts. In the ante iso-alkanes, the alkanes with even-numbered carbons predominate, with the C32 homolog being present in the largest amount. The data provided by Mold et al. (2595) were reproduced by Tso in his 1990 book (3973). 

From the results of studies on the pyrolysis of the tobacco paraffins, which comprise the n-, iso-, and anteiso-alkmes, it was suggested by Lam (2255-2258), Wynder et al. (4356), Wynder and Hoffmann (4319, 4332), and Hoffmann and Wynder (1798) that these components were the major precursors in tobacco of the PAHs in tobacco smoke. However, in 1958, Rayburn and his colleagues (3091, 3092) challenged the proposal that the tobacco alkanes were the major precursors of the smoke PAHs, but their experimental data were not overly conclusive in support of their challenge. Nevertheless, it should be realized that in one sense Rayburn et al. were partly correct as PAH precursors, the tobacco alkanes do contribute to the PAHs in tobacco smoke but their contribution is much less significant than other precursors (the phytosterols and terpenoids such as solanesol) in tobacco [cf. Wright (4282), Rodgman and Cook, (3269, 3286), Severson et al. (3616)]. 

This fraction consists primarily of the n-, iso- (2-methyl-), and anteiso- (3-methyl-) alkanes from Cjj to C40. 

Fig. 12. Principal components analysis of sediment data from Trinity Bay. All data used were concentrations per dry weight. Aik 2 alkanes, AMPL acetone-mobUe polar lipids, i + ai iso + anteiso, Iso 2 isoprenoid hydrocarbons, PAH 2 polycyclic aromatic hydrocarbons, PL phospholipid,POM particulate organic matter, TG triacylglycerol, 16 1/16 16 1/16 0,16/18 2Cij/2Ci8, 18 2 18 2oo6, 18 3 18 3oo3, 20 4 20 4oo6, 20 5 20 5oo3...

Branched-chain alkanes are common in cuticular wax although much less widely distributed than n-alkanes. They comprise a major proportion (nearly 50%) of the alkane fraction from some Nicotiana and Geonium species. Generally, the iso- and anteiso-alkanes (cf Table 1) with odd and even numbers of carbon atoms, respectively, are the main examples although compounds with internal and/or multiple methyl branching and even cycloalkanes have been reported as minor components" " . iso-Alkanes with even-carbon numbers (e.g. C32 and C34 compounds) occur in wax from rose and lavender petals, respectively, and iso and anteiso homologues lower than the range listed in Table 4 (e.g. C21-C23 compounds) have been found in lilac blossom. ... 

Tracer investigations of the formation of n-alkanes (n-C25 to n-C35) and the co-occurring iso, anteiso and branched alkanes in a Nicotiana species were held to support the head to head condensation of small (< C g) units to form the long chains. But this is now generally rejected in view of the weight of evidence supporting the elongation-decarboxylation/decarbonylation pathway, 19 s... 

The latter pathway also appears to be present in several insect species and both and studies revealed that iso- and anteiso-alkanes were formed with incorporation of valine and isoleucine in Musca (housefly) and Blattella (cockroach) species However, the situation seems not necessarily always to be similar in higher plants. " C-Propionate incorporated during chain elongation serves as the donor for the methyl of both the anteiso- and internally branched alkanes (e.g. 3-methyl-C25 etc.) that predominate in Periplanata (cockroach) species and the 3-methyl branch is added just prior to chain completion. In contrast, in another cockroach species (Blattella), this group is introduced early (as in plants) . 

The n-alkanes are hydrocarbons with a straight carbon chain. The iso-alkanes and anteiso-alkanes contain a methyl branch near one of the terminal groups of the molecule ... 

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