N-Alkenes

The olefins are more labile than saturated compounds and therefore the chance of isolation of this group from sea water is low. The 21 6 hexa-olefin present in algae serves some special biochemical function and is a very labile compound even in the dark. It was first isolated from sea water by Blumer (1970) and subsequently detected by Schultz and Quinn (1977) in phytoplankton culture and sea-water samples. 

Many reports have been made on the presence of pristane and phytane. The values of the ratio pristane/phytane given by Ledet and Laseter (1974) for hydrocarbons from the air/sea interface, varying from 1.5 to 2.3, are close to those found for petroleum (1.5—2.5 after Blumer and Sass, 1972) and are consequently indicative of anthropogenic pollution. 

---

The volumes of reaction calculated for the hypothetical cyclizations of n-alkenes to the corresponding cycloalkanes by the use of experimentally observed partial molar volumes190 confirm the trend derived from the ring enlargements shown in Scheme 25. 

Solubility of the reactants and products in the catalyst-containing aqueous phase is another factor to be considered. The solubility of >C3 terminal olefins rapidly decreases with increasing chain length [7] as shown in Table 4.3. The solubihty data in the middle colunm of Table 4.3 refer to room temperature, therefore the values for ethene through 1-butene show the solubility of gases, while the data for 1-pentene through 1-octene refer to solubihties of liquids. For comparison, the solubihties of hquid propene and 1-butene are also shown (third colunm), these were calculated using a known relation between aqueous solubihty and molar volume of n-alkenes [60]. 

Fig. 1 illustrates this dependence for representative liquids. Typically, Gfi and jUp are low for -alkanes, n-alkenes, and aromatics and high for branched compounds with many methyl groups like neopentane. For > 0.1 cm /Vs, the yields for alkanes follow reasonably well a relationship suggested by Jay-Gerin [10] ... 

The most important and dramatic change results when the N-methyl group of morphine is replaced by an N-alkene or N-cyclopropylmethyl group. The resulting compounds show antagonist properties. 

While the above reactions are responsible for meaty flavors, animal fat plays an important role in the formation of the characteristic spedes flavor of cooked meat (14). More than 100 compounds have been identified in heated beef fat, including aldehydes, n-alkanes,n-alkenes, fatty adds, ketones, lactones and heterocyclics (15-18). Of these compounds, the lactones, metltyl ketones and free fatty adds appear to be the most important for desirable meat flavor. 

One of the primary reactions of ionizing radiation with saturated fatty acids is decarboxylation and alkane formation (2). Dimers tend to be produced by reaction of ionizing radiation with unsaturated fatty acids (2). When meats are irradiated C -C 7 n-alkanes, C2-C17 n-alkenes, and C4-Cg iso-alkanes are the predominant products from the lipid fraction (10), Irradiation of the lipoprotein fraction of meat results in the formation of the following volatile compounds Ci-C 7 n-alkanes, C2-C1J n-alkenes, dimethyl sulfide, benzene, and toluene (10). 

From the data and accompanying analysis in a study of catalyzed chain growth polymerization of diethylzinc and n-alkene synthesis , we deduce that the reaction 2... 

The initial step in this kind of reaction is formation of the -n-alkene complex followed by hydride transfer ... 

Lipoprotein C1-C14 n-alkanes (1) C2-C14 n-alkenes (1) Dimethyl sulfide (s) Acetone (m)... 

TABLE 1. Results from the linear regression analysis of equation 4 for 1-n-alkenes (kJmol-1)... 

The effect of excluding the enthalpy of formation of 1-hexene as determined either solely or in part from the combustion measurement21,37 in the regression analyses improves the goodness of fit. Using these regression constants to calculate liquid enthalpies of formation for 1-hexene yields —72.01 kJmol-1 from the 1-n-alkene data in Reference 16 and —72.34 kJmol-1 from similar data in Reference 21. 

A simplifying assumption is that all members of a particular category of alkene, e.g. the 1-n-alkenes, will have about the same enthalpy of hydrogenation and, after enthalpies for a few representative compounds have been precisely measured, the mean value is applicable to other alkenes of the same structural type. This assumption is only true, or approximately so, under well-defined circumstances if applied indiscriminately it can lead to errors in interpreting the energetics of alkenes. The basis for the assumption is clear after recasting equation 5 in the linear form of equation 7. 

The trends in alkene isomer stability can be easily seen in plots of the enthalpies of formation versus the number of carbons, nc (equation 4). For example, in Figure 3 which includes the gaseous 1-, cis- and trans-2-, and the cis- and trans-2-n-alkenes, the relatively more negative enthalpies of formation for the 2- and 3 -n-alkenes show them to be more stable than their 1-n-alkene double bond positional isomers. (Only the C4-C8 1-n-alkene members are shown for clarity.) Another well-known relationship is depicted as well acyclic trans hydrocarbons are more stable than their cis isomers. 

Figure 3 also highlights some curious data which complicates our understanding of alkene stability. That is, although the enthalpies of formation of the fraws-2-n-alkenes are... 

Comparing the effect of the double-bond migration within the identical cr-frameworks of isomeric isoalkyl-1-alkenes and the 2-methyl-1-alkenes, we find that the individual enthalpies of isomerization for Cg-Cs are —10.4, —10.9 and —11.3 kJmol-1. These mono- to disubstituted isomerization enthalpies are very similar to those for isomerization of the 1-n-alkenes to the tram -2-n-alkenes, homologous series which also possess a common structural skeleton. 

---