Polyene hydrocarbons, classes

Millar, J. G. (2000). Polyene hydrocarbons and epoxides a second major class of lepidopteran sex attractant pheromones. Annual Review of Entomology 45 ... 

Two general classes of pheromone compound have been identified in moths, and these have some broad, although not uniform, associations with certain taxa. The polyene hydrocarbons and epoxides of various chain lengths are pheromones found in some subfamilies of the Geometridae and Noctuidae, and in the Arctiidae and Lymantridae (Millar, 2000). These compounds are probably derived from dietary Unoleic and linolenic acids. The other major class of pheromone compounds includes acetate, alcohols, and aldehydes, which are found in the Tortrici-dae, Pyralidae, Gelechiidae, Sessiidae, and Noctuidae. This class of compounds is derived from the insect s fatty acid synthesis pathway, with enzymatic modifications discussed above. Both classes of pheromone are broadly represented in the Noctuidae but are typically found in different subfamilies (Am et al., 1992,2003). 

Very recently, polyenic hydrocarbons were found as a new class of sex pheromones in the family of Geometridae (Lepidoptera) 206>207>. From this class (3Z,6Z,9Z)-... 

Carotenoids are divided into two main classes carotenes and xanthophylls. In contrast to carotenes, which are pure polyene hydrocarbons, xanthophylls contain oxygen in the form of hydroxy, epoxy or 0x0 groups. Some carotenoids of importance to food are presented in the following sections. 

The so-called aromatic hydrocarbons, or arenes, are cyclic unsaturated compounds that have such strikingly different chemical properties from conjugated alkenes (polyenes) that it is convenient to consider them as a separate class of hydrocarbon. The simplest member is benzene, C6H6, which frequently is represented as a cyclic conjugated molecule of three single and three double carbon-carbon bonds. Actually, all the carbon-carbon bonds are equivalent (see Chapter 1) but it is convenient to represent the structure in the manner shown ... 

By connecting double and single bonds, formally five classes of hydrocarbons can be constructed which differ considerably from one another not only chemically and physically but also in terms of their practical significance [1] the linear polyenes 1, the annulenes 2, which consist exclusively of endocyclic double bonds , the radialenes 3, polyolefins which are characterized by semicyclic double bonds, the fulvenes 4, hybrids containing endo-and semicyclic double bonds, and finally, the dendralenes 5 [2] which are acyclic cross-conjugated polyenes... 

Olefins - Acyclic and cyclic hydrocarbons having one or more carbon-carbon double bonds, apart from the formal ones in aromatic compounds. The class olefins subsumes alkenes and cycloalkenes and the corresponding polyenes. [5]... 

Other kinds of aromatic eom])ounds exist besides simple benzene derivatives. Two common types will be covered in this chapter polycyclic fused benzenoid hydrocarbons and other cyclic conjugated polyenes with either more or less than six carbons in the ring. In Chapter 25, a third common class, heterocyclic aromatic compounds, will be pre.sented. 

One final class of compounds that is worthy of mention is the polyenes because it is quite possible that it could make some contribution to the coal precursor. These compounds comprise bicy-clic alkanes, the terpene hydrocarbons, and the carotenoid pigments (Figure 3.18) (Meinschein, 1969 Schwendinger, 1969 Luo et al., 1991). 

Based on the results shown in the table, one can conclude that the largest optical nonlinearity occurs in the longest isomer, system A. This fact confirms the conclusion made for the linear model polyene (Fig. 3.8) and based on the comparison involving its different conformers. The conclusion was generalized for a larger class of condensed aromatic hydrocarbons. 

For moderately complex polyenes, the nodal patterns of the higher molecular orbitals can be difficult to decipher. Fortunately, things are greatly simplified because many systems of interest are members of a class called alternant hydrocarbons (AH). An AH is a system for which all the atoms can be divided into two classes, termed and non- (starred and non-starred), such that no two members of the same class are adjacent. Further, AH are termed "even" or "odd" depending on whether the number of carbon atoms is even or odd, respectively. Figure 14.16 gives examples. Neutral odd AH are radicals. A necessary and sufficient criterion for a non-AH is the presence of an odd-membered ring. 

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